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Design of Riprap Revetment HEC 11Metric Version

Welcometo HEC11-Designof RiprapRevetment.

Table of Contents

Preface

Tech Doc

U.S. - SI Conversions

DISCLAIMER: During the editing of this manual for conversion to an electronic format,the intent has been to convert the publication to the metric system while keeping thedocument as close to the original as possible. The document has undergone editorial updateduring the conversion process.

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Table of Contents for HEC 11-Design of Riprap Revetment (Metric)

List of Figures List of Tables List of Charts & Forms List of Equations

Cover Page : HEC 11-Design of Riprap Revetment (Metric)

Chapter 1 : HEC 11 Introduction 1.1 Scope 1.2 Recognition of Erosion Potential 1.3 Erosion Mechanisms and Riprap Failure Modes

Chapter 2 : HEC 11 Revetment Types 2.1 Riprap 2.1.1 Rock Riprap

2.1.2 Rubble Riprap

2.2 Wire-Enclosed Rock 2.3 Pre-Cast Concrete Block 2.4 Grouted Rock 2.5 Paved Lining

Chapter 3 : HEC 11 Design Concepts 3.1 Design Discharge 3.2 Flow Types 3.3 Section Geometry 3.4 Flow in Channel Bends 3.5 Flow Resistance 3.6 Extent of Protection 3.6.1 Longitudinal Extent

3.6.2 Vertical Extent

3.6.2.1 Design Height

3.6.2.2 Toe Depth

Chapter 4 : HEC 11 Design Guidelines for Rock Riprap 4.1 Rock Size 4.1.1 Particle Erosion

4.1.1.1 Design Relationship

4.1.1.2 Application

4.1.2 Wave Erosion

4.1.3 Ice Damage

4.2 Rock Gradation 4.3 Layer Thickness

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4.4 Filter Design 4.4.1 Granular Filters

4.4.2 Fabric Filters

4.5 Material Quality 4.6 Edge Treatment 4.7 Construction

Chapter 5 : HEC 11 Rock Riprap Design Procedure 5.1 Preliminary Data Analysis 5.2 Rock Sizing (Form 1) 5.3 Revetment Details 5.4 Design Examples 5.4.1 Example Problem #1

5.5.2 Example Problem #2

Chapter 6 : HEC 11 Guidelines for Other Revetments 6.1 Wire-Enclosed Rock 6.1.1 Mattresses

6.1.1.1 Design Guidelines for Rock and Wire Mattresses

6.1.1.2 Construction

6.1.2 Stacked Block Gabions

6.1.2.1 Design Guidelines for Stacked Block Gabions


6.2 Pre-Cast Concrete Blocks 6.2.1 Design Guidelines for Pre-Cast Concrete Blocks

6.2.2 Construction

6.3 Grouted Rock 6.3.1 Design Guidelines for Grouted Rock

6.3.2 Construction

6.4 Concrete Pavement 6.4.1 Design Guidelines for Concrete Pavement

6.4.2 Construction

Appendix A : HEC 11 Suggested Specifications 7.1 Riprap 7.1.1 Description

7.1.2 Materials

7.1.3 Construction Requirements

I. Minimum Quality Standards

II. Minimum Hydraulic Properties

7.1.4 Measurement for Payment

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7.1.5 Basis for Payment

7.2 Wire-Enclosed Rock 7.2.1 Description

7.2.2 Materials




7.3 Grouted Rock Riprap 7.3.1 Description

7.3.2 Materials




7.4 Pre-Cast Concrete Blocks 7.4.1 Description

7.4.2 Materials




7.5 Paved Lining 7.5.1 Description

7.5.2 Materials




Appendix B : HEC 11 Stream Bank Protection Products and Manufacturers 8.1 Gabions 8.2 Cellular Blocks 8.3 Bulkheads 8.4 Filter Fabrics

Appendix C : HEC 11 Design Charts and Forms

Appendix D : HEC 11 Riprap Design Relationship Development 10.1 Basic Relationship 10.2 Design Relationship Calibration 10.3 Conversion to a Velocity Based Procedure 10.4 Comparison with Other Methods

Glossary

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References

Symbols

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List of Figures for HEC 11-Design of Riprap Revetment (Metric)

Back to Table of Contents

Figure 1. Particle Erosion Failure (Modified from Blodgett (6))

Figure 2. Translational Slide Failure (Modified from Blodgett (6))

Figure 3. Modified Slump Failure (Modified from Blodgett (6))

Figure 4. Slump Failure (Modified from Blodgett (6))

Figure 5. Dumped Rock Riprap

Figure 6. Hand-placed Riprap

Figure 7. Plated or Keyed Riprap

Figure 8. Broken Concrete Riprap

Figure 9. Rock and Wire Mattress Revetment

Figure 10. Gabion Basket Revetment

Figure 11. Pre-cast Concrete Block Mat

Figure 12. Grouted Riprap

Figure 13. Concrete Pavement Revetment

Figure 14. Channel Geometry Development

Figure 15. Longitudinal Extent of Revetment Protection

Figure 16. Wave Height Definition Sketch

Figure 17. Definition Sketch; Channel Flow Distribution

Figure 18. Typical Water Surface Profiles Through Bdge Constrictions for Various Types as Indicated(Modified from Bradley (40))

Figure 19. Filter Fabric Placement

Figure 20. Typical Riprap Installation: Plan and Flank Detail

Figure 21. Typical Riprap Installation: End View (bank protection only)

Figure 22. Launching of Riprap Toe Material

Figure 23. Riprap Design Procedure Flow Chart

Figure 24. Riprap Size Form (Form 1); Example 1

Figure 25. Angle of Repose in Terms of Mean Size and Shape of Stone (Chart 4); Example 1

Figure 26. Bank Angle Correction Factor (K1) Nomograph (Chart 4); Example 1

Figure 27. Riprap Size Relationship (Chart 1); Example 1

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Figure 28. Correction Factor for Riprap Size (Chart 2); Example 1

Figure 29. Material Gradation (Form 3); Example 1

Figure 30. Roughness Evaluation (Form 4); Example 1

Figure 31. Channel Cross Section for Example 2, Illustrating Flow and Potential Scour Depths

Figure 32. Toe and Flank Details; Example 2







Figure 39. Revetment Schematic

Figure 40. Rock and Wire Mattress Configurations: (a) Mattress with Toe Apron; (b) Mattress with Toe Wall;(c) Mattress with Toe Wall; and (d) Mattress of Variable Thickness

Figure 41. Rock and Wire Mattress Installation Covering the Entire Channel Perimeter

Figure 42. Typical Detail of Rock and Wire Mattress Constructed from Available Wire Fencing Materials

Figure 43. Mattress Configuration

Figure 44. Flank Treatment for Rock and Wire Mattress Designs: (a) Upstream Face; (b) Downstream Face

Figure 45. Rock and Wire Revetment Mattress Installation

Figure 46. Mattress Placement Underwater by Crane

Figure 47. Pontoon Placement of Wire Mattress

Figure 48. Typical Stacked Block Gabion Revetment Details: (a) Training Wall with Counterforts; (b)Stepped Back Low Retaining Wall with Apron; (c) High Retaining Wall, Stepped-Back Configuration; (d) HighRetaining Wall, Batter Type

Figure 49. Gabion Basket Fabrication

Figure 50. Section Details for (a) Stepped Back and (b) Battered Gabion Retaining Walls

Figure 51. Monoslab Revetment (a) Block Detail and (b) Revetment Detail

Figure 52. Armorflex (a) Block Detail and (b) Revetment Configuration

Figure 53. Petraflex (a) Block Detail and (b) Revetment Configuration

Figure 54. Articulated Concrete Revetment

Figure 55. Tri-lock Revetment

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Figure 56. Grouted Riprap Sections: (a) Section A-A; (b) Section B-B; and (c) Section C-C

Figure 57. Required Blanket Thickness as a Function of Flow Velocity

Figure 58. Concrete Paving Detail: (a) Plan; (b) Section A-A: (c) Section B-B

Figure 59. Concrete Pavement Toe Details

Figure 60. Riprap Design Calibration

Figure 61. Comparison of Procedures for Estimating Stone Size on Channel Bank Based on PermissibleVelocities

Figure 62. Comparison of Procedures for Estimating Stone Size on Channel Bank Based on PermissibleVelocities: Effect of Stability Factor Illustrated

Figure 63. Comparison of Procedures for Estimating Stone Size on Channel Bank Based on PermissibleVelocities: Effect of Flow Depth Illustrated


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Chapter 1 : HEC 11Introduction

Go to Chapter 2

One of the hazards of placing a highway near a river or stream channel is the potential forerosion of the highway embankment by moving water. If erosion of the highway embankment isto be prevented, bank protection must be anticipated, and the proper type and amount ofprotection must be provided in the right locations.

Four methods of protecting a highway embankment from stream erosion are available to thehighway engineer. These are:

Relocating the highway away from the stream.●

Moving the stream away from the highway (channel change).●

Changing the direction of the current with training works.●

Protecting the embankment from erosion.●

1.1 Scope

This circular provides procedures for the design of riprap revetments to be used as channelbank protection and channel linings on larger streams and rivers (i.e., having design dischargesgenerally greater than 1.5 m3/s). For smaller discharges, HEC-15, "Design of RoadsideChannels with Flexible Linings," should be used. Procedures are also presented for riprapprotection at bridge piers and abutments, but for detailed design, HEC-18 should be used.

It is important to recognize the differences between this circular and HEC-15. HEC-15 isintended for use in the design of small roadside drainage channels where the entire channelsection is to be lined. By definition, these channels are usually included within the highwayright-of-way, and the channel gradient typically parallels the highway. The procedures ofHEC-15 are applicable for channels carrying discharges less than 1.5 m3/s where flowconditions are sufficiently uniform so that average hydraulic conditions can be used for design.In contrast, the design guidelines in this circular apply to the design of riprap revetments onlarger streams and rivers where design flow conditions are usually not uniform, and at timescan be quite dynamic. Under these conditions, the assumptions under which the procedures ofHEC-15 were developed become invalid, and local flow conditions must be considered in thedesign process.

The emphasis in this circular is on the design of rock riprap revetments. The remaining sectionsin this chapter cover the recognition of erosion potential, and erosion mechanisms, and riprapfailure modes. Chapter 2 covers common riprap types. Although rock riprap is the primary

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concern here, other riprap types such as gabions, rubble, pre-formed blocks, grouted riprap,and concrete slab revetments are covered. Chapter 3 covers various design concepts relatedto the design of riprap revetments; subject areas covered include flow type, design discharge,section geometry (hydraulic vs. design), flow resistance, local conditions and the extent ofprotection. Design guidelines for rock riprap are presented in Chapter 4; guidelines areprovided for rock size, gradation, blanket thickness, and filter design, as well as for theconstruction and placement of rock riprap revetment. Guidelines for the design of other types ofriprap are presented in Chapter 6.

1.2 Recognition of Erosion Potential

Channel stabilization is essential to the design of any structure in the river environment. Theidentification of the potential for channel bank erosion, and the subsequent need for channelstabilization, is best accomplished through observation. Analytic methods are available for theevaluation of channel stability; however, they should only be used to confirm observations, or incases where observed data are unavailable.

Observations provide the most positive indication of erosion potential. Observations can bebased on historic information, or current site conditions. Aerial photographs, old maps andsurveying notes, and bridge design files and river survey data that are available at Statedepartments of transportation and at Federal agencies, as well as gaging station records andinterviews of long-time residents can provide documentation of any recent and potentiallycurrent channel movement or instabilities.

In addition, current site conditions can be used to evaluate river stability. Even when historicinformation indicates that a channel has been relatively stable in the past, local conditions mayindicate more recent instabilities. Local site conditions which are indicative of channelinstabilities include tipping and falling of vegetation along the bank, cracks along the banksurface, the presence of slump blocks, fresh vegetation laying in the channel near the channelbanks, deflection of channel flows in the direction of the bank due to some recently depositedobstruction or channel course change, fresh vertical face cuts along the bank, locally highvelocities along the bank, new bar formation downstream from an eroding bank, local headcuts,pending or recent cutoffs, etc... It is also important to recognize that the presence of any one ofthese conditions does not in itself indicate an erosion problem; some bank erosion is commonin all channels even when the channel is stable. A more detailed coverage of the analysis ofstream stability through the use of historic and current observations is presented in Shen (1).

Analytic methods for the evaluation of channel stability can be classified as either geomorphicor hydraulic. It is important to recognize that these analytic tools should only be used tosubstantiate the erosion potential indicated through observation. Geomorphic relationshipshave been presented by many investigators, for example Leopold (2), and Lane (3). Morerecently these relationships have been summarized by Brown (4), and Richardson (5).

Hydraulic relationships for evaluating channel stability are based on an analysis of site

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materials, and the ability of these materials to resist the erosive forces produced by a givendesign discharge. This approach uses channel shear stresses and local flow velocities toevaluate the stability of the materials through which the channel is cut. However, this techniqueonly provides a point of reference for evaluating the channel's stability against particle erosion.Particle erosion is only one of several common erosion mechanisms which can cause channelbank instability. Erosion mechanisms will be discussed in the next section.

Complete coverage of geomorphic and hydraulic techniques for evaluating erosion potential isbeyond the scope of this Circular. For additional information it is recommended that the readerrefer to references 2-6.

1.3 Erosion Mechanisms and Riprap Failure Modes

Prior to designing a bank stabilization scheme, it is important to be aware of common erosionmechanisms and riprap failure modes, and the causes or driving forces behind bank erosionprocesses. Inadequate recognition of potential erosion processes at a particular site may leadto failure of the revetment system.

Many causes of bank erosion and riprap failure have been identified. Some of the morecommon include abrasion, debris flows, water flow, eddy action, flow acceleration, unsteadyflow, freeze/thaw, human actions on the bank, ice, precipitation, waves, toe erosion, andsubsurface flows. However, it is most often a combination of mechanisms which cause bankand riprap failure, and the actual mechanism or cause is usually difficult to determine. Riprapfailures are better classified by failure mode. Blodgett (6) has identified classic riprap failuremodes as follows:

Particle erosion.●

Translational slide.●

Modified slump.●

Slump.●

Particle erosion is the most common erosion mechanism. Particle erosion results when thetractive force exerted by the flowing water exceeds the bank materials ability to resistmovement. In addition, if displaced stones are not transported from the eroded area, a moundof displaced rock will develop on the channel bed. This mound has been observed to causeflow concentration along the bank, resulting in further bank erosion.

Particle erosion can be initiated by abrasion, impingement of flowing water, eddy action/reverseflow, local flow acceleration, freeze/thaw action, ice, or toe erosion. Probable causes of particleerosion include:

Stone size not large enough.●

Individual stones removed by impact or abrasion.●

Side slope of the bank so steep that the angle of repose of the riprap material is easily●

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exceeded.

Gradation of riprap too uniform.●

Figure 1 illustrates riprap failure by particle erosion.

Figure 1. Particle Erosion Failure (Modified from Blodgett (6))

A translational slide is a failure of riprap caused by the downslope movement of a mass ofstones, with the fault line on a horizontal plane. The initial phases of a translational slide areindicated by cracks in the upper part of the riprap bank that extend parallel to the channel. Asthe slide progresses, the lower part of riprap separates from upper part, and moves downslopeas a homogeneous body. A resulting bulge may appear at the base of the bank if the channelbed is not scoured.

Translational slides are usually initiated when the channel bed scours and undermines the toeof the riprap blanket. This could be caused by particle erosion of the toe material, or some othermechanism which causes displacement of toe material. Any other mechanism which wouldcause the shear resistance along the interface between the riprap blanket and base material tobe reduced to less than the gravitational force could also cause a translational slide. It hasbeen suggested that the presence of a filter blanket may provide a potential failure plane fortranslational slides (6). Probable causes of translational slides are as follows:

Bank side slope too steep.●

Presence of excess hydrostatic (pore) pressure.●

Loss of foundation support at the toe of the riprap blanket caused by erosion of the lowerpart of the riprap blanket (6).

●

Figure 2 illustrates a typical translational slide.

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Figure 2. Translational Slide Failure (Modified from Blodgett (6))

The failure of riprap referred to as modified slump is the mass movement of material along aninternal slip surface within the riprap blanket; the underlying material supporting the riprap doesnot fail. This type of failure is similar in many respects to the translational slide, but thegeometry of the damaged riprap is similar in shape to initial stages of failure caused by particleerosion. Probable causes of modified slump are:

Bank side slope is so steep that the riprap is resting very near the angle of repose, andany imbalance or movement of individual stones creates a situation of instability for otherstones in the blanket.

●

Material critical to the support of upslope riprap is dislodged by settlement of thesubmerged riprap, impact, abrasion, particle erosion, or some other cause (6).

●

Figure 3 illustrates a modified slump failure.

Figure 3. Modified Slump Failure (Modified from Blodgett (6))

Slump is a rotational-gravitational movement of material along a surface of rupture that has aconcave upward curve. The cause of slump failures is related to shear failure of the underlying

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base material that supports the riprap revetment. The primary feature of a slump failure is thelocalized displacement of base material along a slip surface, which is usually caused by excesspore pressure that reduces friction along a fault line in the base material. Probable causes ofslump failures are:

Nonhomogeneous base material with layers of impermeable material that act as a faultline when subject to excess pore pressure.

●

Side slope too steep, and gravitational forces exceed the inertia forces of the riprap andbase material along a friction plane (6).

●

Figure 4. Slump Failure (Modified from Blodgett (6))

Additional details and examples explaining these erosion mechanisms or failure modes areavailable in reference 6. Note: that the riprap design guidelines presented in this circular applyto particle erosion only. Analysis procedures for other bank failure mechanisms are presentedin reference 31.

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Chapter 2 : HEC 11Revetment Types

Go to Chapter 3

The types of slope protection or revetment discussed in this circular include:Rock riprap.●

Rubble riprap.●

Wire-enclosed rock (Gabions).●

Pre-formed blocks.●

Grouted rock.●

Paved Lining.●

Descriptions of each of these revetment types are included in the sections. Note: wire-enclosedrock, pre-formed block, grouted rock, and concrete slab revetments listed above are rigid or ofonly limited flexibility, and do not conform to the definition of riprap. These revetments havebeen historically discussed with flexible riprap, and therefore are included in this circular.

2.1 Riprap

Riprap has been described as a layer or facing of rock, dumped or hand-placed to preventerosion, scour, or sloughing of a structure or embankment. Materials other than rock are alsoreferred to as riprap; for example, rubble, broken concrete slabs, and preformed concreteshapes (slabs, blocks, rectangular prisms, etc.). These materials are similar to rock in that theycan be hand-placed or dumped onto an embankment to form a flexible revetment.

In the context of this circular, riprap is defined as:

"A flexible channel or bank lining or facing consisting of a well graded mixture ofrock, broken concrete, or other material, usually dumped or hand-placed, whichprovides protection from erosion."

As described above, riprap is a flexible revetment. Flexibility of the riprap mass is due toindividual particles acting independently within the mass. In the past, the term "riprap" has oftenbeen extended to include mortared and grouted riprap, concrete riprap in bags (sackedconcrete), and concrete slab riprap, as well as other rigid revetments. However, the materialswhich make up these revetments are not singular; as a result, the entire revetment must act ormove together. These revetment materials will not be considered as riprap here since they falloutside the definition given above.

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2.1.1 Rock Riprap

Rock riprap is the most widely used and most desirable type of revetment in theUnited States. It is compatible with most environmental settings. The term "riprap" ismost often used to refer to rock riprap. For purposes of description, rock riprap isfurther subdivided by placement method into dumped riprap, hand-placed riprap,and plated riprap.

Dumped riprap is graded stone dumped on a prepared slope in such a mannerthat segregation will not take place. Dumped riprap forms a layer of loose stone;individual stones can independently adjust to shifts in or movement of the basematerial. The placement of dumped riprap should be done by mechanized means,such as crane and skip, dragline, or some form of bucket. End dumping from trucksdown the riprap slope causes segregation of the rock by size, reducing its stability,and therefore, should not be used as a means of placement. The effectiveness ofdumped riprap has been well established where it is properly installed, of adequatesize, and suitable size gradation. Advantages associated with the use of dumpedrock riprap include:

The riprap blanket is flexible and is not impaired or weakened by minormovement of the bank caused by settlement or other minor adjustments.

●

Local damage or loss can be repaired by placement of more rock.●

Construction is not complicated.●

When exposed to fresh water, vegetation will often grow through the rocks,adding esthetic and structural value to the bank material and restoring naturalroughness.

●

Riprap is recoverable and may be stockpiled for future use. Note: that slopefailure processes as discussed in Chapter 1 will cause riprap damage.

●

One drawback to the use of rock riprap revetments is that they are more sensitivethan some other bank-protection schemes to local economic factors. For example,freight/haul costs can significantly affect the cost of these revetments. Figure 5illustrates a dumped riprap installation.Arch

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Figure 5. Dumped Rock Riprap

Hand-placed riprap is stone laid carefully by hand or by derrick following a definitepattern, with the voids between the larger stones filled with smaller stones and thesurface kept relatively even. The need for interlocking stone in a hand-placedrevetment requires that the stone be relatively uniform in size and shape (square orrectangular).

Advantages associated with the use of hand-placed riprap include:The even interlocking surface produces a neat appearance and reduces flowturbulence at the water revetment interface.

●

The support provided by the interlocking of individual stones permits the useof hand-placed riprap revetments on steeper bank slopes than is possible withthe same size loose stone riprap.

●

With hand-placed riprap, the blanket thickness can usually be reduced to 150to 300 mm less than a loose riprap blanket, resulting in the use of less stone(25).

●

Disadvantages associated with hand-placed riprap include:Installation is very labor-intensive, resulting in high costs.●

The interlocking of individual rocks in hand-placed revetments results in a lessflexible revetment; as mentioned above, a small shift in the base material ofthe bank can cause failure of large segments of the revetment.

●

By their nature, hand-placed rock riprap revetments are more expensive torepair than are loose rock revetments.

●

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Figure 6. Hand-placed Riprap

Plated or keyed riprap is similar to hand-placed riprap in appearance andbehavior, but different in placement method. Plated riprap is placed on the bankwith a skip and then tamped into place using a steel plate, thus forming a regular,well organized surface. Experience indicates that during the plating operation, thelarger stones are fractured, producing smaller rock sizes to fill voids in the riprapblanket.

Advantages and disadvantages associated with the use of plated riprap are similarto those listed above for hand-placed riprap. As with hand-placed riprap, riprapplating permits the use of steeper bank angles, and a reduction in riprap layerthickness (usually 150-300 mm less than loose riprap). Experience also indicatesthat riprap plating also permits the use of smaller stone sizes when compared withloose riprap. Like hand-placed riprap, riprap plating results in a more rigid ripraplining than loose riprap. This makes it susceptible to failure as a result of minor banksettlement. However, plated riprap installation is not as labor-intensive as that ofhand-placed riprap. Figure 7 illustrates a plated riprap installation underconstruction. Arch

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Figure 7. Plated or Keyed Riprap

2.1.2 Rubble Riprap

Types of rubble which have been used as riprap include rock spoils, brokenconcrete, and steel furnace slag.

Rock spoils are often available from road cut or other excavation sites.

Broken concrete is available in areas undergoing widespread urbanrenewal involving the demolition of buildings and other structures madefrom concrete.

Steel furnace slag is sometimes available in the vicinity of steelsmelting plants.

Because it is usually considered to be a waste material, rubble is a veryeconomical riprap material. Advantages and disadvantages to the useof rubble are quite similar to those listed previously for rock riprap.

The successful use of rubble as riprap requires good control on material quality.The quality of a rubble material includes its shape, specific weight, gradation, anddurability (resistance to weathering). The shape of rubble riprap is often a problem(particularly concrete rubble). The length to width ratio of any riprap material shouldbe 1:3 or less (19) . Plating of rubble riprap will often break the material sufficientlyto reduce the length to width ratio of most of the material to less than 1:3. Thematerial's specific weight can be accounted for in the design procedure for sizingthe material. However, in many instances the rubble material will not contain anappropriate mix of particle sizes to form an adequate riprap material. This can beovercome by a crushing operation, or by plating the rubble after placement. (As

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indicated previously, riprap plating fractures the larger riprap material; the smallerfractured material then fills the voids between the larger material, improving thegradation of the final installation.) The recommended placement method for rubbleriprap is plating.

The lack of adequate material durability can cause the failure of rubble riprap. Rockspoils consisting of a high percentage of shale or other materials consisting ofweakly layered structures are not suitable. Also, materials subject to chemicalbreakdown or high rates of weathering are not suitable. Figure 8 illustrates a sitewhere broken concrete was used as the riprap material.

Figure 8. Broken Concrete Riprap

2.2 Wire-Enclosed Rock

Wire-enclosed rock, or gabion, revetments consist of rectangular wire mesh baskets filled withrock. These revetments are formed by filling pre-assembled wire baskets with rock, andanchoring to the channel bottom or bank. Wire-enclosed rock revetments are generally of twotypes distinguished by shape:

Rock and Wire-Mattresses, In mattress designs, the individual wire mesh units are laidend to end and side to side to form a mattress layer on the channel bed or bank. Thegabion baskets comprising the mattress generally have a depth dimension which is muchsmaller than their width or length.

1.

Block Gabions, On the other hand, are more equidimensional, having depths that areapproximately the same as their widths, and of the same order of magnitude as theirlengths. They are typically rectangular or trapezoidal in shape. Block gabion revetmentsare formed by stacking the individual gabion blocks in a stepped fashion.

2.

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As revetments, wire-enclosed rock has limited flexibility. They will flex with bank surfacesubsidence; however, if excessive subsidence occurs, the baskets will span the void until thestresses in rock-filled baskets exceed the tensile strength of the wire strands. At this point thebaskets will fail.

The conditions under which wire-enclosed rock is applicable are similar to those of otherrevetments. However, their economic use is limited to locations where the only rock availableeconomically is too small for use as rock riprap slope protection.

The primary advantages of wire-enclosed rock revetments include:Their ability to span minor pockets of bank subsidence without failure.●

The ability to use smaller, lower quality, and less dense, rock in the baskets.●

The primary disadvantages of wire-enclosed rock revetments include:Susceptibility of the wire baskets to corrosion and abrasion damage.●

High labor costs associated with fabricating and filling the wire baskets.●

More difficult and expensive repair than standard rock protection.●

Less flexibility than standard rock protection.●

Besides its use as a general bank revetment, wire-enclosed rock in the form of eithermattresses or blocks is also used as bank toe protection. In some instances the wire-enclosedrock is used alone for protection of the bank also. In other cases, the wire-enclosed rock isused as toe protection along with some other bank revetment.

The most common failure mechanism of wire basket revetments has been observed to befailure of the wire baskets. Failure from abrasion and corrosion of the wire strands has evenbeen found to be a common problem when the wire is coated with plastic. The plastic coating isoften stripped away by abrasion from sand, gravel, cobbles, or other sediments carried innatural stream flows (particularly at and near flood stages). Once the wire has been broken, therock in the baskets is usually washed away. To avoid the problem of abrasion and corrosion ofthe wire baskets, it is recommended that wire-enclosed rock revetments not be used on lowerportions of the channel bank in environments subject to significant abrasion or corrosion.

An additional failure mechanism has been observed when the wire basket units are used inhigh-velocity, steep-slope environments. Under these conditions, the rock within individualbaskets shifts downstream, deforming the baskets as the material moves. The movement ofmaterial within individual baskets will sometimes result in exposure of filter or base material.Subsequent erosion of the exposed base material can cause failure of the revetment system.

A common misconception with rock and gabion revetments is that a heavy growth of vegetationwill occur through the stone and wire mesh. Experience indicates that in many cases there isnot sufficient soil retained within the baskets to promote significant vegetative growth. Theexception to this is in areas subjected to significant deposition of fine materials (such as in thevicinity of bars). In areas where the baskets are frequently submerged by an active flow,vegetative growth will not be promoted.

Wire-enclosed rock revetments are classified by geometry as mattress or block type

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revetments. Rock and wire mattress revetments consist of flat wire baskets. The individualmattress sections are laid end to end and side to side on a prepared channel bed or bank toform a continuous mattress. The individual basket units are attached to each other andanchored to the base material. Figure 9 illustrates a typical rock and wire mattress installation.Block gabion revetments consist of rectangular wire baskets which are stacked in astepped-back fashion to form the revetment surface. Gabion baskets are best used as bankprotection where the bank is too steep for conventional rock riprap revetments. Gabion basketscan be stacked to form almost vertical banks (looking much like retaining walls) making themuseful in areas where the banks cannot economically be graded to the stable slope required forother riprap types. Figure 10 illustrates a typical block gabion installation.

Figure 9. Rock and Wire Mattress Revetment

Figure 10. Gabion Basket Revetment

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2.3 Pre-Cast Concrete Block

Pre-cast concrete block revetments are a recent development. The pre-formed sections whichcomprise the revetment systems are butted together or joined in some fashion; as such, theyform a continuous blanket or mat. The concrete blocks which make up the mats differ in shapeand method of articulation, but share certain common features. These features includeflexibility, rapid installation, and provisions for establishment of vegetation within the revetment.The permeable nature of these revetments permits free draining of the bank materials; theflexibility, although limited, allows the mattress to conform to minor changes in the bankgeometry. Their limited flexibility, however, makes them subject to undermining in environmentscharacterized by large fluctuations in the surface elevation of the channel bed and/or bank.Unlike wire-enclosed rock, the open nature of the pre-cast concrete blocks does promotevolunteering of vegetation within the revetment.

The most significant drawbacks to the use of pre-cast concrete blocks are their limited flexibilityand cost. As discussed above, their limited flexibility makes them subject to undermining inenvironments characterized by dynamic bed level fluctuations; failures have been observedwhere a corner or edge of the mattress is undercut, resulting in complete failure of therevetment. Pre-cast concrete block designs have also been shown to be expensive. For thisreason, their use is usually limited to large rivers, areas where structures of significant valueneed to be protected, or where riprap is not readily available. Figure 11 illustrates a revetmentconsisting of pre-cast, interlocking blocks.

Figure 11. Pre-cast Concrete Block Mat

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2.4 Grouted Rock

Grouted rock revetment consists of rock slope-protection having voids filled with concrete groutto form a monolithic armor. Grouted rock is a rigid revetment; it will not conform to changes inthe bank geometry due to settlement. As with other monolithic revetments, grouted rock isparticularly susceptible to failure from undermining and the subsequent loss of the supportingbank material. Although it is rigid, grouted rock is not extremely strong; therefore, the loss ofeven a small area of bank support can cause failure of large portions of the revetment.

The use of grouted rock is usually confined to areas where rock of sufficient size for ordinaryrock-slope protection is not economically available, or where a reasonably smooth revetmentsurface is desired (for reasons of safety or flow efficiency). The use of grouted rock can reducethe quantity of rock required; grouting anchors the rock, and integrates a greater material massto resist the hydraulic forces it is exposed to. Also, if the embankment material is fine grained,grouting will eliminate the need for filter material that may be necessary with other rockslope-protection.

Grouting can double the cost per unit volume of stone. However, the ability to use smallerstones and thinner stone layers in grouted rock revetments than in ungrouted rock riprapoffsets some of the additional cost of the grout. Figure 12 illustrates a grouted riprapinstallation.

Figure 12. Grouted Riprap

2.5 Paved Lining

Concrete pavement revetments are cast in place on a prepared slope to provide the necessarybank protection. Like grouted rock, concrete pavement is a rigid revetment which does not

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conform to changes in bank geometry due to a removal of foundation support by subsidence,undermining, outward displacement by hydrostatic pressure, slide action, or erosion of thesupporting embankment at its ends. The loss of even small sections of the supportingembankment can cause complete failure of the revetment system. Concrete pavementrevetments are also among the most expensive streambank protection designs. In the past,concrete pavement has been best utilized as a subaqueous revetment (on the bank below thewater surface) with vegetation or some other less expensive upper-bank treatment.

Concrete pavement revetments are required in some instances. The implied structural integrityof the concrete pavements makes them resistant to damage from debris, ice, and other floatingobjects. Their smooth surface also makes them useful in situations where hydraulic efficiency isof prime importance. They can also be erected on steep bank angles, making them useful insituations where bank grading is not practical. When installed properly, concrete pavement canprovide a long useful life, requiring only a minimum of maintenance. Figure 13 illustrates atypical concrete slab revetment installation.

Figure 13. Concrete Pavement Revetment


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Chapter 3 : HEC 11Design Concepts

Go to Chapter 4

Design concepts related to the design of riprap revetments are discussed in this chapter.Subjects covered include:

Design discharge.●

Flow types.●

Section geometry.●

Flow in channel bends.●

Flow resistance.●

Extent of protection.●

3.1 Design Discharge

Design flow rates for the design or analysis of highway structures in the vicinity of rivers andstreams usually have a 10 to 50-year recurrence interval. In most cases, these discharge levelswill also be applicable to the design of riprap and other revetment systems. However, thedesigner should be aware that in some instances, a lower discharge may produce hydraulicallyworse conditions with respect to riprap stability. It is suggested that several discharge levels beevaluated to ensure that the design is adequate for all discharge conditions up to that selectedas the design discharge for structures associated with the riprap scheme.

A discussion of techniques and procedures for the evaluation of discharge frequency(recurrence interval), risk, and least total economic cost is beyond the scope of this manual.These subjects are covered in detail in references 7 and reference 8 as well as numerous otherhydrology texts.

3.2 Flow Types

Open channel flow can be classified from three points of reference. These are:Uniform, gradually varying, or rapidly varying flow.●

Steady or unsteady flow.●

Subcritical or supercritical flow.●

These flow states, and procedures for identifying them are covered in most open channel flowtexts (for example Chow (9), and Simons and Senturk (10)), as well as in numerous generalreferences on open channel flow (for example U.S. Dept. of Agriculture (11), and Richardsonet. al. (12)).

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Design relationships presented in this manual are based on the assumption of uniform, steady,subcritical flow. These relationships are also valid for gradually varying flow conditions. Whilethe individual hydraulic relationships presented are not in themselves applicable to rapidlyvarying, unsteady, or supercritical flow conditions, procedures are presented for extending theiruse to these flow conditions.

Rapidly varying, unsteady flow conditions are common in areas of flow expansion, flowcontraction, and reverse flow. These conditions are common at and immediately downstream ofbridge crossings. Supercritical or near supercritical flow conditions are common at bridgeconstrictions and on steep sloped channels.

It has been observed that fully developed supercritical flow rarely occurs in natural channels(13). However, steep channel flow, and flow through constrictions is often in a transitional flowstate between subcritical and supercritical. Experimental work conducted by the U.S. ArmyCorps of Engineers (14) indicates that this transition zone occurs between Froude numbers of0.89 and 1.13. When flow conditions are within this range, an extremely unstable conditionexists in which the inertia and gravity force s are unbalanced. This causes excessive waveaction, hydraulic jumps, localized changes in water-surface slope, and extreme flow turbulence.

Non-uniform, unsteady, and near supercritical flow conditions create stresses on the channelboundary that are significantly different from those induced by uniform, steady, subcritical flow.These stresses are difficult to assess quantitatively. The stability factor method of riprap designpresented in Chapter 4 provides a means of adjusting the final riprap design (which is based onrelationships derived for steady, uniform, subcritical flow) for the uncertainties associated withthese other flow conditions. The adjustment is made through the assignment of a stabilityfactor. The magnitude of the stability factor is based on the level of uncertainty inherent in thedesign flow conditions.

3.3 Section Geometry

Riprap design procedures presented in this manual requires input channel cross-sectiongeometry. The cross section geometry is necessary to establish the hydraulic designparameters (such as flow depth, topwidth, velocity, hydraulic radius, etc.) required by the riprapdesign procedures, as well as to establish a construction cross section for placement of therevetment material. When the entire channel perimeter is to be stabilized, the selection of anappropriate channel geometry is only a function of the desired channel conveyance propertiesand any limiting geometric constraints. However, when the channel bank alone is to beprotected, the design must consider the existing channel bottom geometry.

The development of an appropriate channel section for analysis is very subjective. The intent isto develop a section which reasonably simulates a worst case condition with respect to riprapstability. Information which can be used to evaluate channel geometry includes current channelsurveys, past channel surveys (if available), and current and past aerial photos. In addition, theeffect channel stabilization will have on the local channel section must be considered.

The first problem arises when an attempt is made to establish an existing channel bottom

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profile for use in design. A survey of the channel at the location of interest would seeminglyprovide the necessary geometry. However, it has been found that on an annual basis, the crosssection area, hydraulic radius, topwidth, mean depth, and maximum depth vary from theirlong-term means by an average of plus 52 percent and minus 41 percent (15). This suggeststhat cross section data surveyed at a site during a given year may vary as much as 50 percentfrom the long-term mean. Therefore, a single channel profile is usually not enough to establishthe design cross section.

In addition to current channel surveys, historic surveys can provide valuable information. Acomparison of current and past channel surveys at the location provides information on thegeneral stability of the site, as well as a history of past channel geometry changes. Often, pastsurveys at a particular site will not be available. If this is the case, past surveys at other sites inthe vicinity of the design location can be used to evaluate past changes in channel geometry.

The final consideration must always be an evaluation of the impact channel stabilization willhave on the channel geometry. Stabilizing a channel's banks will in most instances cause adeepening of the channel. This phenomenon is most notable at channel bends, but is also ofsignificant concern in straight reaches. Bank stabilization has been observed to increase themaximum-to-average depth ratio to approximately 1.7 (15). The maximum-to-average depthratio is computed using annual average or near bank-full stage conditions. Themaximum-to-average depth ratio should be computed based on the current channel geometry.It should be assumed that the cross section will eventually develop to this condition. For theanalysis, the section geometry should be deepened at the thalweg to a depth that wouldproduce a maximum-to-average depth ratio of 1.7 or greater.

The process of developing an appropriate channel geometry is illustrated in Figure 14a. Figure14b, and Figure 14c, Figure 14a illustrates the location of the design site at position '2' alongRoute 1. The section illustrated in Figure 14c was surveyed at this location, and represents thecurrent condition. No previous channel surveys were available at this site. However, data fromseveral old surveys were available in the vicinity of a railroad crossing upstream (location 1).Figure 14b illustrates this survey data. The surveys in Figure 14b indicate that there is a trendfor the thalweg of the channel to migrate within the right half of the channel. Since location 1and 2 are along bends of similar radii, it can be reasonably assumed that a similarphenomenon occurs at location 2. A thalweg located immediately adjacent to the channel bankreasonably represents the worst case hydraulically for the section at location 2. Therefore, thesurveyed section at location 2 is modified to reflect this. In addition, the maximum section depth(located in the thalweg) is increased to reflect the effect of stabilizing the bank. The maximumdepth in the thalweg is set to 1.7 times the average depth of the original section. The finalmodified section geometry is illustrated in Figure 14c. Note: it is assumed that the averagedepth before modification of the section is the same as the average depth after modification.

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3.4 Flow in Channel Bends

Flow conditions in channel bends are complicated by the distortion of flow patterns in thevicinity of the bend. In long, relatively straight channels, the flow conditions are uniform, andsymmetrical about the center line of the channel. However, in channel bends, the centrifugalforces and secondary currents produced lead to non-uniform and non-symmetrical flowconditions.

Two aspects of flow in channel bends impact the design of riprap revetments. First, specialconsideration must be given to the increased velocities and shear stresses that are generatedas a result of non-uniform flow in bends. In the design relationship presented in Chapter 4, thisis accomplished by using the maximum cross section depth in place of an average hydraulicradius.

Superelevation of flow in channel bends is another important consideration in the design ofriprap revetments. Although the magnitude of superelevation is generally small when comparedwith the overall flow depth in the bend (usually less than 0.3 m) it should be considered whenestablishing freeboard limits for bank protection schemes on sharp bends. The magnitude ofsuperelevation at a channel bend may be estimated for subcritical flow by the followingequation:

Z = C [(Va2 T)/(gRo)] (1)

where:

Z = superelevation of the water surface (m),C = coefficient that relates free vortex motion to velocity streamlines for unequal radius of curvature,Va = mean channel velocity (m/s),T = water-surface width at section (m),g = gravitational acceleration (m/s2),Ro = the mean radius of the channel centerline at the bend (m).

The coefficient C has been recently evaluated (15). The value was found to rangebetween 0.5 and 3.0, with an average of 1.5.Arch

ived

Figure 14. Channel Geometry Development

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3.5 Flow Resistance

The hydraulic analysis performed as a part of the riprap design process requires the estimationof Manning's roughness coefficient. Roughness evaluation can be determined usingcomparative photographs (see reference 17 and 34), or resistance equations based on physicalcharacteristics of natural channels (see reference 17 and 11). Physical characteristics uponwhich the resistance equations are based include the channel base material, surfaceirregularities, variations in section geometry, obstructions, vegetation, channel meandering,flow depth, and channel slope. In addition, seasonal changes in these factors must also beconsidered. Procedures for the evaluation of reach average roughness coefficients are detailedin reference 17, "Guide for Selecting Manning's Roughness Coefficients for Natural Channels."Additional guidance is provided here for the appropriate selection of a base 'n' to be used in theprocedure.

The base 'n' is primarily a function of the material through which the channel is cut. References17 and 11 present several methods for the establishment of a base 'n' including tabular listings,photographic comparisons, and computational methods. These methods are applicable forchannels cut through natural materials. For riprap lined channels, Equation 2, Equation 3, andEquation 4 are recommended. Equation 2 and Equation 3 provide estimates of Manning'sroughness coefficient based on laboratory and natural channel data (5).

The following form can be used to calculate Manning's values:

for 1.5 < da/D50 < 185

n = 0.023 d0.167 for 185 < da/D50 < 30,000

(2)

(3)

where:

da = the average channel flow depth (m),D50 = the median bed material size (m).

The accuracy of Equation 2 and Equation 3 are dependent on good estimates ofmedian bed material size. On high gradient streams it is extremely difficult to obtaina good estimate of the median bed material size. For high gradient streams withslopes greater than 0.002 and bed material larger than .06 m (gravel, cobble, orboulder size material), it is recommended that the relationship given in Equation 4be used to evaluate the base 'n' (13).n = 0.3225 Sf 0.38 R - 0.16 (4)

where:

Sf = friction slope,

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R = hydraulic radius, (m).

Figure 15. Longitudinal Extent of Revetment Protection

3.6 Extent of Protection

Extent of protection refers to the longitudinal and vertical extent of protection required toadequately protect the channel bank.

3.6.1 Longitudinal Extent

The longitudinal extent of protection required for a particular bank protectionscheme is highly dependent on local site conditions. In general, the revetmentshould be continuous for a distance greater than the length that is impacted bychannel-flow forces severe enough to cause dislodging and/or transport of bankmaterial. Although this is a vague criteria, it demands serious consideration. Reviewof existing bank protection sites has revealed that a common misconception instreambank protection is to provide protection too far upstream and not far enoughdownstream.

One criterion for establishing the longitudinal limits of protection required isillustrated in Figure 15. As illustrated, the minimum distances recommended forbank protection are an upstream distance of 1.0 channel width and a downstreamdistance of 1.5 channel widths from corresponding reference lines (see Figure 15).All reference lines pass through tangents to the bend at the bend entrance or exit.

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This criterion is based on analysis of flow conditions in symmetric channel bendsunder ideal laboratory conditions. Real-world conditions are rarely as simplistic. Inactuality, many site-specific factors have a bearing on the actual length of bank thatshould be protected. A designer will find the above criterion difficult to apply onmildly curving bends or on channels having irregular, non-symmetric bends. Also,other channel controls (such as bridge abutments) might already be producing astabilizing effect on the bend so that only a part of the channel bend needs to bestabilized. In addition, the magnitude or nature of the flow event might only causeerosion problems in a very localized portion of the bend, requiring that only a shortchannel length be stabilized. Therefore, the above criteria should only be used as astarting point. Additional analysis of site-specific factors is necessary to define theactual extent of protection required.

Field reconnaissance is a useful tool for the evaluation of the longitudinal extent ofprotection required, particularly if the channel is actively eroding. In straight channelreaches, scars on the channel bank may be useful to help identify the limitsrequired for channel bank protection. In this case, it is recommended that upstreamand downstream limits of the protection scheme be extended a minimum of onechannel width beyond the observed erosion limits.

In curved channel reaches, the scars on the channel bank can be used to establishthe upstream limit of erosion. Here again, a minimum of one channel width shouldbe added to the observed upstream limit to define the limit of protection. Thedownstream limit of protection required in curved channel reaches is not as easy todefine. Since the natural progression of bank erosion is in the downstreamdirection, the present visual limit of erosion might not define the ultimatedownstream limit. Additional analysis based on consideration of flow patterns in thechannel bend may be required. Flow dynamics in channel bends are covered indetail in reference 18. Included are discussions of flow and erosion processes inchannel bends, and how the flow dynamics change with flow magnitude, flow stage,and whether or not the flow event is occurring on the rising or falling limb of therunoff hydrograph.

As indicated previously, the extent of bank protection can also be influenced byexisting channel controls. The most common situation encountered is the existenceof a bridge somewhere along the bend. If the bridge has an abutment immediatelyadjacent to the channel bank, it will act as a control point with respect to channelstability. The location of the bridge abutment (or other channel control such as arock outcrop) will usually define the downstream limit of active channel movement.If the control point does not cause significant flow contraction, or there is nosignificant flow expansion downstream of the control, the bank revetment should beterminated approximately one channel width downstream of the control. However, ifsignificant flow contraction and/or expansion is occurring in the vicinity of thecontrol, the protection should be continued downstream for a distance equal to fourtimes the constricted channel width at the control.

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3.6.2 Vertical Extent

The vertical extent of protection required of a revetment includes design height andfoundation or toe depth.

3.6.2.1 Design Height

The design height of a riprap installation should be equal to the design highwaterelevation plus some allowance for freeboard. Freeboard is provided to ensure thatthe desired degree of protection will not be reduced by unaccounted factors. Somesuch factors include:

Wave action (from wind or boat traffic).●

Superelevation in channel bends.●

Hydraulic jumps.●

Flow irregularities due to piers, transitions, and flow junctions.●

In addition, erratic phenomena such as unforeseen embankment settlement, theaccumulation of silt, trash, and debris in the channel, aquatic or other growth in thechannels, and ice flows should be considered when setting freeboard heights. Also,wave run-up on the bank must be considered.

The amount of freeboard cannot be fixed by a single, widely applicable formula. Theimpact from each of the items listed above must be considered individually, andtheir joint impact estimated to determine an adequate freeboard estimate. Guidanceis available in the literature for computing elevations for some of the conditionslisted above. Procedures for estimating the height of waves due to hydraulic jumps,and flow irregularities (due to piers, transitions, and flow junctions) are available inreferences 9 and 12, as well as most standard open channel flow texts. In addition,Equation 1 can be used for estimating superelevation heights.

The prediction of wave heights from wind and boat generated waves is not asstraightforward as other wave sources. Figure 16 provides a definition sketch for thewave height discussion to follow. The height of boat generated waves must beestimated from observations. The height of wind generated waves is a function offetch length, wind speed, wind duration, and the depth of the water body. Detailedprocedures for estimating design wind speeds and durations, and for determiningthe controlling factors in the development of wind generated waves are provided inreference 20. In design situations where wind generated waves are considered tobe of significant importance, it is recommended that the procedures of reference 20be followed. The significance of wind generated waves can be estimated usingChart 6 of Appendix C.

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Figure 16. Wave Height Definition Sketch

Chart 6 in Appendix C is provided as a tool for estimating wave heights due to windgenerated waves. Chart 6 is entered with estimates of the design wind speed,duration, and fetch length to determine an estimate of the generated wave height.The chart is limited to wind speeds of 72.4 km/h and fetch lengths of 16.1 km. Ifestimated wave heights from Chart 6 are greater than .61 m, the procedures ofreference 20 should be used to refine the design wave height. Note: that Chart 6 isonly intended to provide an initial estimate of wind generated wave heights.

Wind data for use in determining design wind speeds and durations is usuallyavailable from primary weather stations, airports, and major dams and reservoirs.The data is often incomplete, and is reported in varying formats. To get an initialestimate of wave heights from Chart 6, a reasonable estimate of wind speed shouldbe used. If the resulting estimated wave height is greater than .61 m, procedures inreference 20 should be used to refine wind speed estimates.

In addition to wave height estimates, it is necessary to estimate the magnitude ofwave runup, which results when waves impact the bank. Detailed procedures forestimating wave runup are presented in references 14 and 20 . Wave runup is afunction of the design wave height, the wave period, bank angle, and the banksurface characteristics (as represented by different revetment materials). Chapter 7of reference 20 provides detailed procedures for estimating wave runup based onthe factors described above. The detailed procedures of reference 20 are notjustified for most highway applications. For wave heights less than 0.61 m, waverunup can be computed using Chart 8 and Table 9. Correction factors are proved inTable 9 for reducing the runup magnitude for other revetment materials. The

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correction factor from Table 9 is multiplied times the wave height to get the resultingwave runup (R).

As indicated, there are many factors which must be considered in the selection ofan appropriate freeboard height. As a minimum, it is recommended that a freeboardelevation of .30 to .61 m be used in unconstricted reaches, and .61 to .91 m inconstricted reaches (These criteria are consistent with those presented by theFederal Emergency Management Agency). When computational proceduresindicate that additional freeboard may be required, the greater height should beused. In addition, it is recommended that the designer observe wave and flowconditions during various seasons of the year (if possible), consult existing records,and interrogate persons who have knowledge of past conditions when establishingthe necessary vertical extent of protection required for a particular revetmentinstallation.

3.6.2.2 Toe Depth

The undermining of revetment toe protection has been identified as one of theprimary mechanisms of riprap revetment failure. In the design of bank protection,estimates of the depth of scour are needed so that the protective layer is placedsufficiently low in the streambed to prevent undermining. The ultimate depth ofscour must consider channel degradation as well as natural scour and fillprocesses.

Channel degradation is a morphologic change in a river system which ischaracterized by the general reduction in channel base level. A complete coverageof geomorphic analysis procedures is beyond the scope of this manual. Detailedcoverage of this subject is included in references 4 and 5.

The relationships presented in Equation 5 can be used to estimate the probablemaximum depth of scour due to natural scour and fill phenomenon in straightchannels, and in channels having mild bends. Equation 5 is based on datapresented by Blodgett (15). In application, the depth of scour, ds, determined fromEquation 5 should be measured from the lowest elevation in the cross section. It isassumed that the low point in the cross section may eventually move adjacent tothe riprap (even if this is not the case in the current survey).

The following form can be used to calculate D50: ds = 3.66 m for D50 < 0.0015 m, ds = 1.74 D50 -0.11 for D50 > 0.0015 m,

(5)

where:

ds = estimated probable maximum depth of scour (m) D50 = median diameter of bed material (m)

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The depth of scour predicted by Equation 5 must be added to the magnitude ofpredicted degradation and local scour (if any) to arrive at the total required toedepth.

Go to Chapter 4

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Chapter 4 : HEC 11Design Guidelines for Rock Riprap

Go to Chapter 5

As defined in Chapter 2, rock riprap consists of a well graded mixture of rock, broken concrete,or other material, dumped or hand placed to prevent erosion, scour, or sloughing of a structureor embankment. In the context of this chapter, the term rock riprap is used to refer to both rockand rubble riprap.

Rock riprap is the most widely used and desirable type of revetment in the United States. Theterm "riprap" connotes rock riprap. The effectiveness of rock riprap has been well establishedwhere it is properly installed, of adequate size and suitable gradation. Riprap materials includequarry-run rock, rubble, or other locally available materials. Performance characteristics of rockand rubble riprap are reviewed in Section 2.1.1.

This chapter contains design guidelines for the design of rock riprap. Guidelines are providedfor:

Rock size,●

Rock gradation,●

Riprap layer thickness,●

Filter design,●

Material quality,●

Edge treatment, and●

Construction considerations.●

In addition, typical construction details are illustrated. In most cases, the guidelines presentedapply equally to rock and rubble riprap. Sample specifications for rock riprap are included inAppendix A.

4.1 Rock Size

The stability of a particular riprap particle is a function of its size, expressed either in terms of itsweight or equivalent diameter. In the following sections, relationships are presented forevaluating the riprap size required to resist particle and wave erosion forces.

4.1.1 Particle Erosion

In Chapter 1, riprap failure modes were identified as particle erosion, translationalslide, modified slump, and slump. Translational slide, modified slump, and slump areslope or soils processes. Particle erosion is a hydraulic phenomenon which results

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when the tractive force exerted by the flowing water exceeds the riprap materialsability to resist motion. It is this process that the riprap design relationshipspresented in this section were developed for.

Two methods or approaches have been used historically to evaluate a materialsresistance to particle erosion. These methods are:

1. Permissible velocity approach:

Under the permissible velocity approach the channel is assumed stable ifthe computed mean velocity is lower than the maximum permissiblevelocity.

2. Permissible tractive force (shear stress) approach.

The tractive force (boundary shear stress) approach focuses on stressesdeveloped at the interface between flowing water and materials formingthe channel boundary.

By Chow's definition, permissible tractive force is the maximum unit tractive forcethat will not cause serious erosion of channel bed material from a level channel bed(9) . Permissible tractive force methods are generally considered to be moreacademically correct; however, critical velocity approaches are more readilyembraced by the engineering community.

4.1.1.1 Design Relationship

A riprap design relationship that is based on tractive force theory yet hasvelocity as its primary design parameter is presented in Equation 6. Thedesign relationship in Equation 6 is based on the assumption of uniform,gradually varying flow. The derivation of Equation 6 along with acomparison with other methods is presented in Appendix D. Chart 1 inAppendix C presents a graphical solution to Equation 6. Equation 7 canbe solved using Chart 3 and Chart 4 of Appendix C.

The following form can be used to calculate D50: D50 =0.00594 Va3/(davg0.5 K11.5 )

where:

D50 = the median riprap particle size (m); C = correction factor (described below); Va = the average velocity in the main channel (m/s); davg = the average flow depth in the main flow channel (m); and K1 is defined as:

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K1 = [1- (sin2 θ/sin2φ)]0.5

where:

θ = the bank angle with the horizontal; and φ = the riprap material's angle of repose.

(7)

The average flow depth and velocity used in Equation 6 are mainchannel values. The main channel is defined as the area between thechannel banks (see Figure 17).

Figure 17. Definition Sketch; Channel Flow Distribution

Equation 6 is based on a rock riprap specific gravity of 2.65, and astability factor of 1.2. Equation 8 and Equation 9 present correctionfactors for other specific gravities and stability factors.

The following form can be used to calculate D50: Csg = 2.12/(Ss - 1)1.5

where:

Ss = the specific gravity of the rock riprap.

(8)

Csf = (SF/1.2)1.5

where:

SF = the stability factor to be applied.

(9)

The correction factors computed using Equation 8 and Equation 9 aremultiplied together to form a single correction factor C. This correctionfactor, C, is then multiplied by the riprap size computed from Equation 6

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to arrive at a stable riprap size. Chart 2 in Appendix C provides a solutionto Equation 8 and Equation 9 using correction factor C.

The stability factor, SF, used in Equation 6 and Equation 9 requiresadditional explanation. The stability factor is defined as the ratio of theriprap material's critical shear stress and the average tractive forceexerted by the flow field. As long as the stability factor is greater than 1,the critical shear stress of the material is greater than the flow inducedtractive stress, the riprap is considered to be stable. As mentionedabove, a stability factor of 1.2 was used in the development of Equation6.

The stability factor is used to reflect the level of uncertainty in thehydraulic conditions at a particular site. Equation 6 is based on theassumption of uniform or gradually varying flow. In many instances, thisassumption is violated or other uncertainties come to bear. For example,debris and/or ice impacts, or the cumulative effect of high shear stressesand forces from wind and/or boat generated waves. The stability factor isused to increase the design rock size when these conditions must beconsidered. Table 1 presents guidelines for the selection of anappropriate value for the stability factor.

Table 1. Guidelines for the Selection of Stability FactorsCondition Stability

Factor RangeUniform flow; Straight or mildly curving reach (curve radius/channel width > 30); Impactfrom wave action and floating debris is minimal; Little or no uncertainty in designparameters.

1.0-1.2

Gradually varying flow; Moderate bend curvature (30 > curve radius/channel width > 10);Impact from waves or floating debris moderate.

1.3-1.6

Approaching rapidly varying flow; Sharp bend curvature(10 > curve radius/channel width);Significant impact potential from floating debris and/or ice; Significant wind and/or boatgenerated waves (.30 - .61 m)); High flow turbulence; Turbulently mixing flow at bridgeabutments; Significant uncertainty in design parameters.

1.6-2.0

4.1.1.2 Application

Application of the relationship in Equation 6 is limited to uniform orgradually varying flow conditions. That is in straight or mildly curvingchannel reaches of relatively uniform cross section. However, designneeds dictate that the relationship also be applicable in nonuniform,rapidly varying flow conditions often exhibited in natural channels withsharp bends and steep slopes, and in the vicinity of bridge piers andabutments.

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Research efforts to define stable riprap size relationships for nonuniform,rapidly varying flow conditions have been limited. Recently work byWang and Shen (35) and Maynord (36) has shed some light on thevariability of the Shields parameter for large particle sizes in highReynold's Number flows. However, no definitive relationship has beenpresented.

To fill the need for a design relationship that can be applied at sharpbends and on steep slopes in natural channels, and at bridge abutments,it is recommended that Equation 6 be used with appropriate adjustmentsin velocity and/or stability factor as outlined in the following sections.

Channel Bends: At channel bends modifications to the stability factorare recommended based on the ratio or curve radius to channel width(R/W) as indicated in the following:

R/W Stability Factor> 30 1.2

30 > R/W > 10 1.3 - 1.6< 10 1.7

Steep Slopes: Flow conditions in steep sloped channels are rarelyuniform, and are characterized by high flow velocities and significant flowturbulence. In applying Equation 6 to steep slope channels, care must beexercised in the determination of an appropriate velocity. Whendetermining the flow velocity in steep sloped channels, it isrecommended that Equation 4 be used to determine the channelroughness coefficient. It is also important to thoughtfully consider theguidelines for selection of stability factors as presented in Table 1.

Bridge piers: The FHWA is currently evaluating various equations forselection of riprap at bridge piers. Present research indicates thatvelocities in the vicinity of the base of a pier can be related to the velocityin the channel upstream of the pier. For this reason, the interimprocedure presented below is recommended for designing riprap atpiers:

Determine the D50 size of the riprap using the rearranged Ishbashequation to solve for stone diameter, for fresh water:

●

The following form can be used to calculate D50:

(10)

where:

D50 = average stone diameter (m),

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V = velocity against stone (m/s) ,s = specific gravity of riprap material ,g = acceleration due to gravity m/s2

To calculate V, first determine the velocity of flow just upstream of thepier. This may be approximated by the velocity in the contracted section.Then multiply this value by a factor of 1.5 to 2.0 to approximate thevelocity of flow at the base of the pier. Note: preliminary research byFHWA indicates that a factor of about 1.5 may be a reasonable designvalue.

Provide a mat width that extends horizontally at least two times thepier width measured from the pier face.

●

Place the mat below the streambed a depth equivalent to theexpected scour. The thickness should be three stone diameters ormore.

●

Abutments: When applying Equation 6 for riprap design at abutments avelocity in the vicinity of the abutment should be used instead of theaverage section velocity. The velocity in the vicinity of bridge abutmentsis a function of both the abutment type (vertical, wingwalled, orspillthrough), and the amount of constriction caused by the bridge.However, information documenting velocities in the vicinity of bridgeabutments is currently unavailable. Until such information becomesavailable, it is recommended that Equation 6 be used with a stabilityfactor of 1.6 to 2.0 for turbulently mixing flow at bridge abutments. Note:the average velocity and depth used in Equation 6 for riprap design atbridge constrictions for abutment protection is the average velocity anddepth in the constricted cross section at the bridge. Flow profiles atbridge sections are nonuniform as indicated in Figure 17. Therecommended procedure for computing the average depth and velocityat bridge constrictions is:

Model the reach in the vicinity of the crossing using WSPRO (38),HEC-2 (39), or some other model with bridge loss routines.

1.

Compute the average depth and velocity in the constriction as theaverage of the depth and velocity for modeled cross sections at theentrance to, and exit from the bridge constriction (in the vicinity ofcross sections 2 and 3 as illustrated in Figure 18).

2.

In instances where resources are not available to model flow conditionsat the constriction as indicated above, normal depth and its associatedflow velocity for the constricted section can be used.

As outlined above, the average section flow depth and velocity used inEquation 6 are main channel values. The main channel is typically

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defined as the area between the channel banks (see Figure 17).However, when the bridge abutments are located on the floodplain asufficient distance from the natural channel banks so as not to beinfluenced by main channel flows, the average depth and velocity on thefloodplain within the constricted section should be used in the riprapdesign relationship. Most standard computerized bridge backwaterroutines provide the necessary depths and velocities as a part of theirstandard output. If hand normal depth computations are being used, thecomputations must consider conveyance weighted effects of bothfloodplain, and main channel flows. See reference 5 or standard openchannel hydraulics texts for appropriate procedures.

When there is no overbank flow and the bridge spillthrough abutment onthe channel bank matches the slope of the main channel banksupstream and downstream, use the design procedure withoutmodification.

4.1.2 Wave Erosion

Waves generated by wind or boat traffic have also been observed to cause bankerosion on inland waterways. The most widely used measure of riprap's resistanceto wave is that developed by Hudson (24). The so-called Hudson relationship isgiven by the following equation:

The following form can be used to calculate Wave Erosion:W50 =(γs H3)/(2.20 [Ss - 1]3 cotθ)

where:

H = the wave height; and the other parameters areas defined previously.

(11)

Assuming

Ss = 2.65 and γs =2647 kg/m3 = 25952 N/m3

Equation 11 can be reduced to:

W50 = 267.8 H3/cotθ

In terms of an equivalent diameter Equation 12 can be reduced to:

(12)

D50 = 0.57H/cot 1/3θ (13)

Methods for estimating a design wave height are presented in Section 3.6.2.Equation 13 is presented in nomograph form in Chart 7 of Appendix C. Equation 12and Equation 13 can be used for preliminary or final design when H is less than 1.52m, and there is no major overtopping of the embankment.

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4.1.3 Ice Damage

Ice can affect riprap linings in a number of ways. Moving surface ice can causecrushing and bending forces as well as large impact loadings. The tangential flow ofice along a riprap lined channel bank can also cause excessive shearing forces.Quantitative criteria for evaluating the impact ice has on channel protection schemesare unavailable. However, historic observations of ice flows in New England riversindicate that riprap sized to resist design flow events will also resist ice forces.

For design, consideration of ice forces should be evaluated on a case by casebases. In most instances, ice flows are not of sufficient magnitude to warrantdetailed analysis. Where ice flows have historically caused problems, a stabilityfactor of 1.2 to 1.5 should be used to increase the design rock size. Note: theselection of an appropriate stability factor to account for ice generated erosiveproblems should be based on the designer's experience.

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layer, or from 100 mm to 200 mm for individual layers of a multiple layer blanket.Where the gradation curves of adjacent layers are approximately parallel, thethickness of the blanket layers should approach the minimum. The thickness ofindividual layers should be increased above the minimum proportionately as thegradation curve of the material comprising the layer departs from a parallel pattern.

4.4.2 Fabric Filters

Synthetic fabric filters have found considerable use as alternatives to granular filters.Advantages and disadvantages of synthetic fabric filters are discussed below.

Advantages relevant to the use of fabric filters have been identified:Installation is generally quick and labor-efficient.●

Fabric filters are more economical than granular filters.●

Fabric filters have consistent and more reliable material quality.●

Fabric filters have good inherent tensile strength.●

Local availability of suitable granular filter material is no longer a designconsideration when using fabric filters.

●

Disadvantages include:Filter fabrics can be difficult to lay under-water.●

Installation of some fabrics must be undertaken with care to prevent undueultraviolet light exposure.

●

The life of the fabric in a soil environment is as yet unproven over the lifetimeof a normal engineering project.

●

Bacterial activity within the soil or upon the filter can control the hydraulicresponses of a fabric filter system.

●

Experimental evidence indicates that when channel banks are subjected towave action, non-cohesive bank material has a tendency to migrate downslopebeneath fabric filters; this tendency was not observed with granular filters.

●

Fabric filters may induce translational or modified slump failures when usedunder rock riprap installed on steep slopes (6).

●

Fabric filters have a definite advantage over granular filters in many applications.The primary justification is economic; the U.S. Army Corps of Engineers has foundgeotextiles to be more cost effective than granular filters in many instances. This isparticularly true in areas where a good source of gravel is not convenient (25).

The function of fabric filters is to provide both drainage and filtration. In other words,the fabric must allow water to pass (drainage) while retaining soil properties(filtration). Therefore, both functions must be considered and must perform properlyduring the design life of the system. Despite their advantages, fabric filters, likegranular filters, still require engineering design. Unless proper fabric pipingresistance, clogging resistance, and construction strength requirements are

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specified, it is doubtful that desired results will be obtained. Also, constructioninstallation and monitoring must be provided to see that the materials have beeninstalled correctly.

Detailed criteria for the design of fabric (geotextile) filters are presented in reference26 provides a summary of the minimum criteria from reference 26 for noncritical andnonsevere applications (as described in the notes for Table 8). The quality andhydraulic properties criteria in Table 8 are applicable for most riprap designsituations. However, for critical applications, the more detailed criteria of reference26 are recommended.

Filter fabric placement. To provide good performance, a properly selected clothshould be installed with due regard for the following precautions:

Heavy riprap may stretch the cloth as it settles, eventually causing bursting ofthe fabric in tension. A 100-150 mm gravel bedding layer should be placedbeneath the riprap layer for riprap gradations having D50 greater than 0.91 m.

●

The filter cloth should not extend into the channel beyond the riprap layer;rather, it should be wrapped around the toe material as illustrated in Figure 19.

●

Adequate overlaps must be provided between individual fabric sheets. Forclass I revetments this can be as little as 300 mm, and may increase to asmuch as 0.91 m for large underwater revetments.

●

A sufficient number of folds should be included during placement to eliminatetension and stretching under settlement.

●

Securing pins with washers are recommended at .61 to 1.52 m intervals alongthe midpoint of the overlaps.

●

Proper stone placement on the filter requires beginning at the toe andproceeding up the slope. Dropping stone from heights greater than 0.61 m canrupture fabrics (greater drop heights are allowable under water).

●

Figure 19. Filter Fabric Placement

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4.5 Material Quality

Riprap consists of rock, broken concrete, or other rubble type materials. The most satisfactorytype of riprap is rock riprap. Any of these forms of riprap can be used as long as adequatecontrol is maintained on the materials quality and gradation. Gradation requirements werediscussed in Section 4.2.

Stone or other material used for riprap is exposed to environmental extremes. Therefore, theriprap should be hard, dense and durable. In addition, it should be resistant to weathering, freefrom overburden, spoil, shale and organic material. Rock or rubble that is laminated, fractured,porous, or otherwise physically weak is unacceptable as rock slope protection.

Stone shape is another important factor in the selection of an appropriate riprap material. Ingeneral, riprap constructed with angular material has the best performance. Round material canbe used as riprap provided it is not placed on slopes greater than 1V:3H. Flat slab-like stonesshould be avoided since they are easily dislodged by the flow. Broken concrete must beadequately broken or fragmented before it is acceptable as a riprap material. An approximateguide to stone shape is that neither the breadth or thickness of a single stone should be lessthan one-third its length.

4.6 Edge Treatment

The edges of riprap revetments (head, toe, and flanks) require special treatment to preventundermining.

Flanks: The flanks of the revetment should be designed as illustrated in Figure 20. Theupstream flank is illustrated in part (b) and the downstream flank in part (c) of Figure 20. Analternative to the upstream flank section illustrated in part (b) is to fill the compacted fill area withriprap.

Toe: Undermining of the revetment toe is one of the primary mechanisms of riprap failure. Thetoe of the riprap should be designed as illustrated in Figure 21. The toe material should beplaced in a toe trench along the entire length of the riprap blanket as illustrated in Figure 21.Where a toe trench cannot be dug, the riprap blanket should terminate in a thick, narrow stonetoe at the level of the streambed (see alternate design in Figure 21). Care must be taken duringthe placement of the stone to ensure that the toe material does not mound and form a low dike;a low dike along the toe could result in flow concentration along the revetment face which couldstress the revetment to failure. In addition, care must be exercised to ensure that the channel'sdesign capability is not impaired by placement of too much riprap in a toe mound.

The size of the toe trench or the alternate stone toe is controlled by the anticipated depth ofscour along the revetment. As scour occurs (and in most cases it will) the stone in the toe willlaunch into the eroded area as illustrated in Figure 22. Observation of the performance of thesetypes of rock toe designs indicates that the riprap will launch to a final slope of approximately1V:2H. The volume of rock required for the toe must be equal to or exceed one and one-half

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times the volume of rock required to extend the riprap blanket (at its design thickness and on aslope of 1V:2H) to the anticipated depth of scour. Establishing a design scour depth is coveredin Section 3.6.2.2.

4.7 Construction Additional considerations related to the construction of riprap revetments include bank slope orangle, bank preparation, and riprap placement.

Bank slope: A primary consideration in the design of stable riprap bank protection schemes isthe slope of the channel bank. For riprap installations, the maximum recommended face slope is1V:2H.

Bank Preparation: The bank should be prepared by first clearing all trees and debris from thebank, and grading the bank surface to the desired slope. In general, the graded surface shouldnot deviate from the specified slope line by more than 150 mm. However, local depressionslarger than this can be accommodated since initial placement of filter material and/or rock for therevetment will fill these depressions. In addition, any large boulders or debris found buried nearthe edges of the revetment should be removed.

Riprap Placement: The common methods of riprap placement are hand placing; machineplacing, such as from a skip, dragline, or some form of bucket; and dumping from trucks andspreading by bulldozer. Hand placement produces the best riprap revetment, but it is the mostexpensive method except when labor is unusually cheap. Steeper side slopes can be used withhand placed riprap than with other placing methods. Where steep slopes are unavoidable (whenchannel widths are constricted by existing bridge openings or other structures, and whenrights-of-way are costly), hand placement should be considered. In the machine placementmethod, sufficiently small increments of stone should be released as close to their final positionsas practical. Rehandling or dragging operations to smooth the revetment surface tend to resultin segregation and breakage of stone, and can result in a rough revetment surface. Stoneshould not be dropped from an excessive height as this may result in the same undesirableconditions. Riprap placement by dumping and spreading is the least desirable method as a largeamount of segregation and breakage can occur. In some cases, it may be economical toincrease the layer thickness and stone size somewhat to offset the shortcomings of thisplacement method. Arch

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Figure 20. Typical Riprap Installation: Plan and Flank DetailArchive

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Figure 21. Typical Riprap Installation: End View (bank protection only)

Figure 22. Launching of Riprap Toe Material


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Chapter 5 : HEC 11Rock Riprap Design Procedure

Go to Chapter 6

Rock riprap design procedure outlined in the following sections is comprised of three primary sections: preliminary data analysis,rock sizing, and revetment detail design. A section is devoted to each component. A flow chart of the design procedure is presentedin Figure 23. The individual steps in the procedure are numbered consecutively throughout each of the sections. Notes andmiscellaneous comments are inserted between steps where additional explanation is required. Reference is made at each step to thesection or chart that contains the information necessary for that step. Form 1 and Form 2 in Appendix C provide a useful format forrecording data at each step of the analysis. The final section of this chapter presents design examples which demonstrate the designprocedure presented.

5.1 Preliminary Data Analysis

Step 1. Compile all necessary field data including (channel cross section surveys, soils data, aerial photographs, history ofproblems at site, etc.).

Step 2. Determine design discharge. Section 3.1.

Step 3. Develop design cross section(s). Section 3.3.

5.2 Rock Sizing (Form 1)Note: The rock sizing procedures described in the following are designed to prevent riprap failure from particle erosion.

Step 4. Compute design water surface.

When evaluating the design water surface, Manning's "n" should be estimated using procedures from Section 3.5. If a ripraplining is being designed for the entire channel perimeter, an estimate of the rock size may be required to determine theroughness coefficient "n". (Form 4).

.

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If the design section is a regular trapezoidal shape, and flow can be assumed to be uniform, use design charts such as those inreference (37).

B.

If the design section is irregular or flow is not uniform, backwater procedures must be used to determine the design watersurface. Computer methods such as WSPRO(38) and HEC-2 (39) are recommended.

C.

Any backwater analysis conducted must be based on conveyance weighting of flows in the main channel, right bank and leftbank.

D.

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Figure 23. Riprap Design Procedure Flow Chart

Step 5. Determine design average velocity and depth.

Average velocity and depth should be determined for the design section in conjunction with the computations ofstep 4. In general, the average depth and velocity in the main flow channel should be used.

.

If riprap is being designed to protect channel banks, abutments, or piers located in the floodplain, averagefloodplain depths and velocities should be used.

B.

Step 6. Compute the bank angle correction factor K1 Section 4.1.1, Equation 7, Chart 3.

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Step 7. Determine riprap size required to resist particle erosion equation.See Section 4.1.1, Equation 6, Chart 1.

Initially assume no corrections..

Evaluate correction factor for rock riprap specific gravity andstability factor (C = Csg Csf).

B.

If designing riprap for piers or abutments apply pier/abutmentcorrection (CP/A) or 3.38.

C.

Compute corrected rock riprap size as:D.

D'50 = C(CP/A)D50

Step 8. If entire channel perimeter is being stabilized, and an assumed D50 was used in determination of Manning's'n' for backwater computations, return to step 4 and repeat steps 4 through 7.

Step 9. If surface waves are to be evaluated: Form 2.

Determine significant wave height (see Section 3.6.2, and Chart 6)..

Use Chart 7 to determine rock size required to resist wave action (see Section 4.1.2, Equation 12).B.

Step 10. Select final D50 riprap size, set material gradation (see Section 4.2 and Form 3), and determine riprap layerthickness (see Section 4.3).

5.3 Revetment Details

Step 11. Determine longitudinal extent of protection required Section 3.6.1.

Step 12. Determine appropriate vertical extent of revetment Section 3.6.2.

Step 13. Design filter layer. Section 4.4. Form 5.

Determine appropriate filter material size, and gradation.

Determine layer thickness.

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Step 14. Design edge details (flanks and toe). Section 4.6.

5.4 Design ExamplesThe following design examples illustrate the use of the design methods and procedures outlined above. Two examples are given;Example 1 illustrates the design of a riprap lined channel section. Example 2 illustrates the design of riprap as bank protection. In theexamples, the steps correlate with the design procedure outline presented above. Reference is also made to appropriate sections fromthe manual which outline procedures used. Computations are also shown on appropriate forms.


A 381 m channel reach is to be realigned to make room for the widening of an existing highway. Realignment of thechannel reach will necessitate straightening the channel and reducing its length from 381 m to 305 m. The channel is tobe sized to carry 141.6 m3/s within its banks. Additional site conditions are as follows:

Flow conditions can be assumed to be uniform or gradually varying;●

The existing channel profile dictates that the straightened reach be designed at a uniform slope of 0.0049;●

The natural soils are gap graded from medium sands to coarse gravels as illustrated in the gradation curve ofFigure 29. The gradation curve indicates the following soil characteristics:

●

D85 = 0.032 m1.

D50 = 0.018 m2.

D15 = 0.001 m3.

K (permeability) = 3.5 X 10-4 m/s●

Available rock riprap has a specific gravity of 2.65.●

Design a stable trapezoidal riprap lined channel for this site. Design forms and chart used in this example are reproducedin Figure 24, Figure 25, Figure 26, Figure 27, Figure 28, Figure 29, and Figure 30.

Step 1. Compile Field Data

See given information for this example.●

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Other field data would typically include site history, geometric constraints, roadway crossing profiles, sitetopography, etc.

●

Step 2. Design Discharge. See Section 3.1.

Given as 119 m3/s.●

Discharge in main channel equals the design discharge since entire design discharge is to be contained in channelas specified.

●

Step 3. Design Cross Section. See Section 3.3.

As specified, a trapezoidal section is to be designed.●

Initially assume a trapezoidal section with 6.1 m bottom width and 1V:2H side slopes. See Form 1.●

Step 4. Compute Design Water Surface.

(a) Determine roughness coefficient using Form 4 (see Section 3.5).

Using procedures of reference 17

n = (nb +n1 +n2 +n3 +n4 )m

nb : base channel "n"

slope = 0.0049 > 0.002

Therefore, use Equation 4 for computation of the base n value.

nb = 0.3225 Sf0.38 R-0.16

assume R = 2.43 m

nb = 0.037

n1 : irregularity factor

n1 = 0.00 smoothest Channel obtainable in natural materials

n2 : variation in cross section

n2 = 0.00 size and shape of cross section constant

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n3 : effect of obstructions

n3 = 0.00 no obstructions

n4 : amount of vegetation

n4 = 0.003 minor (assumes some growth within riprap)

m : degree of meander

m = 1.0 straight reach

n = (0.037+0.00+0.00+0.00+0.003)1

n = 0.040

(b) Compute flow depth.

Solve Manning's equation for normal depth(use computer programs, or charts and tablesavailable in open channel hydraulics textsof procedure manuals).

●

Q = (1/n) A R2/3 S1\2

d = 3.60 m Column 1 of Form 1

Compute hydraulic radius to compare with theassumed value used in Step 4a (use computerprograms, available charts and tables, ormanually compute).

●

R = A/P

R = 47.9/22.2=2.16

R = 2.16 not equal to Rassumed = 2.43

Therefore, return to Step 4a

nb = 0.3225 (0.0049)0.38 (2.16)-0.16

nb = 0.038

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n = (0.038 + 0.003)1 = 0.041

which is approximately equal to 0.040 used above, therefore,

d = 3.60 m (Column 1 of Form 1)

Step 5. Determine Design Parameters

A = 3.6(3.6(4) + 6.1 + 6.1)/2 = 47.8 m2 (Column 2 of Form 1.)

Va = Q/A = 141.6/47.8 = 2.96 m/s (Column 3 of Form 1.)

da = d = 3.60 m(uniform channel bottom) (Column 4 of Form 1)

Step 6. Bank Angle Correction Factor. See Section 4.1.1.

θ = 1V:2H (Column 5 of Form 1).

f = 41° (Figure 25)

K1 = 0.73 (Figure 26)

Step 7. Determine riprap size See Section 4.1.

(a) Using Chart 1 (Figure 27)

for channel bed D50 = 0.085 m (Column 8 of Form 1)for channel bank D50 = 0.131 m (Column 8 of Form 1)

(b) Riprap specific gravity = 2.65 (given) (Column 10 of Form 1)

Stability factor = 1.2 (uniform flow, little or no uncertainty in design)

C = 1 Chart 2, Figure 28.

(c) no piers or abutments to evaluate for this example, therefore

Cp/a = 1 (Column 12 of Form 1)

(d) Corrected riprap size

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For channel bed

D'50 = D50 = 0.085 m (Column 13 of Form 1)

For channel banks

D'50 = D50 = 0.131 m (Column 13 of Form 1)

Step 8. not applicable

Step 9. Surface wave See Section 4.1.2.

Surface waves determined not to be a problem at this site.

Step 10. Select Design Riprap Size, Gradation, and Layer Thickness

D50 size: Recommend AASHTO Face Class riprap

D50 = 0.29 m (for entire perimeter) See Figure 24.

Gradation: See Form 1, Figure 24 See Section 4.2.

Layer thickness (T): See Section 4.3.

T = 2 D50 =0.29 m

T = 0.58 m

or

T = D100 = 0.40 m

Use T = 0.60 m See Figure 24.

Step 11. Longitudinal Extent of Protection See Section 3.6.1.

Riprap lining to extend along entire length of straightened reach.

Step 12. Vertical Extent of Protection See Section 3.6.2.

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Riprap entire channel perimeter to top-of-bank.

Step 13. Filter Layer Design See Section 4.4.

(a) Filter material size:

For the riprap to soil interface:

and

Therefore, a filter layer is needed.

Try 50 mm uniformly graded coarse gravel filter(gradation characteristics as illustrated in Form 3,Figure 29).

For the filter to soil interface:

and

Therefore, filter to soil interface is OK.

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For the riprap to filter interface:

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and

Therefore, the 50 mm filter material is adequate.

(b) Filter layer thickness:

Since soil gradation curve and filter layer gradation curve are notapproximately parallel, use layer thickness of 200 mm.

Step 14. Edge Details see Section 4.6

Line entire perimeter; edge details as per Figure 20(also see sketch on Form 1, Figure 24).

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Figure 25. Angle of Repose in Terms of Mean Size andShape of Stone (Chart 4); Example 1

The following charts may benefit from the following D50 Calculation form:Archive

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Figure 26. Bank Angle Correction Factor (K1) Nomograph (Chart 3); Example 1Archive

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Figure 28. Correction Factor for Riprap Size (Chart 2); Example 1Archive

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Figure 29. Material Gradation (Form 3); Example 1Arch

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Figure 30. Roughness Evaluation (Form 4); Example 1


The site illustrated in Figure 14 and discussed in Section 3.3 is migrating laterally towards Route 1 (see Figure 14a).Design a riprap revetment to stabilize the active bank erosion at this site. Additional site conditions are as follows:

flow conditions are gradually varying;●

channel characteristics are as described in Section 3.3;●

Topographic survey indicates:●

channel slope = 0.00241.

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channel width = 91.4 m2.

bend radius = 365.8 m3.

channel bottom is armored with cobble size material having a D50 of approximately 0.15 m;●

bank soils are silty sands as illustrated in the gradation curve of Figure 38 (Form 3). The gradation curve indicatesthe following soil characteristics:

●

D85 = 0.0013 m1.

D50 =0.0005 m2.

D15 = 0.00014 m3.

K (permeability) = 1 x 10-6 m/s

Available rock riprap has a specific gravity of 2.60, and is described as angular.●

field observations indicate that the banks are severely cut just downstream of the bend apex; erosion was alsoobserved downstream the bend exit and upstream to the bend quarter points;

●

bank height along cut banks is approximately 2.7 m.●

Design forms and charts used in this example are reproduced on the pages following this example.

Step 1. Compile Field Data.

See given information for this example.●

See site history given in Section 3.3.●

Step 2. Design Discharge. See Section 3.1.

Given as 1,112 m3/s.●

From backwater analysis of this reach, it is determined that the discharge confined to the main channel (Qmc) is

982.6 m3/s.

●

Step 3. Design Cross Section. See Section 3.3.

Only the channel bank is to be stabilized; therefore, the channel section will consist of the existing channel withthe bank graded to an appropriate angle to support the riprap revetment. Figure 31 illustrates the existing channelsection.

●

To minimize loss of bank vegetation, and limit the encroachment of the channel on adjacent lands, a 1V:2H bankslope is to be used.

●

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As given, the current bank height along the cut banks is 2.7 m.●

Step 4. Compute Design Water Surface.

(a) Determine roughness coefficient. See Section 3.5.

Using procedures of Form 4.

n = (nb +n1 +n2 +n3 +n4)m

nb: base channel "n"

slope = 0.0024 > 0.002

Therefore, use Equation 4 for computation of the base n value.

nb = 0.3225 Sf0.38 R-0.16

assume R = 3.05 m

nb = 0.028

n1: irregularity factor

n1 = 0.005 minor - moderately eroded side slopes

n2: variation in cross section

n2 = 0.005 occasional shape changes cause flow shifting

n3: effect of obstructions

n3 = 0.000 no obstructions

n4: amount of vegetation

n4 = 0.000 no vegetation

m: degree of meander

m = 1.1 minor to appreciable

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n = (0.028 + 0.005 + 0.005 + 0.000 + 0.000) 1.10

n = 0.042

This represents the average reach "n" used in the backwater analysis.

(b)Compute flow depth.

Flow depth determined from backwater analysis. The maximum main channel depth was determined to be:●

dmax = 4.6 m Column 1 of Form 1

Hydraulic radius for main channel

R = 3.2 m (from backwater analysis)

Rassumed (3 m) is approximately equal to R actual, therefore, "n"as computed is OK.

Step 5. Determine Other Design Parameters.

From backwater analysis: (all main channel values).

A =838.2 m2 Column 2 of Form 1

Va = 3.84 m/s Column 3 of Form 1

da = d = 3.66 m Column 4 of Form 1

Step 6. Bank Angle Correction Factor. See Section 4.1.1.

θ = 1V:2H Column 5 of Form 1

φ = 41o Column 6 of Form 1 (from chart 4, Figure 33)

K1 = 0.73 Column 7 of Form 1 (from chart 3, Figure 34)

Step 7. Determine riprap size. See Section 4.1.

(a) Using Chart 1 (Figure 35).

D50 = 0.27 m Column 8 of Form 1

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(b) Riprap specific gravity = 2.60 (given). Column 10 of Form 1.

Stability factor = 1.6. Column 9 of Form 1. (gradually varying flow, sharp bend - bend radius to width = 4).

C = 1.6 See Figure 36

(c) no piers or abutments to evaluate for this example, therefore:

Cp/a = 1 Column 12 of Form 1

(d) Corrected riprap size:

D'50 = D50 = (1.6)(1.0) = 0.44 m Column 13 of Form 1

Step 8. not applicable.

Step 9. Surface waves. See Section 4.1.2.

Surface waves determined not to be a problem at this site.

Step 10. Select Design Riprap Size, Gradation, and Layer Thickness.

D50 size: Recommend AASHTO 0.23 Metric Ton class riprap

D50 = 0.55 m

Gradation: See Form 1 , Figure 37 See Section 4.2

Layer thickness (T): See Section 4.3

T = 2 D50 = 2(0.55)

T = 1.10 m

or

T = D100 = 0.68 m

Use T = 1.10 m

Step 11. Longitudinal Extent of Protection. See Section 3.6.1.

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Field observations indicate that the banks are severely cut just downstream of the bend apex; erosion wasalso observed downstream to the bend exit and upstream to the bend quarter points.

Establish longitudinal limits of protection to extend to a point 91.4 m (W) upstream of the bank entrance,and to a point 137 m (1.5 W) downstream of the bend exit.

Step 12. Vertical Extent of Protection. See Section 3.6.2.

Riprap entire channel bank from top-of-bank to below depth of anticipated scour. Scour depth evaluated asillustrated in Section 3.6.2.2:

ds = 2.0 D50-0.11 (Equation 5)

ds = 2.0(0.55)-0.11 =2.14 m

Adding this to the observed maximum depth yields a potential maximum scour depth of:

4.6 + 2.1 = 6.7 m

The bank material should be run to this depth, or a sufficient volume of stone should be placed at the banktoe to protect against the necessary depth of scour.

Step 13. Filter Layer Design. See Section 4.4.

(a) Filter material size: Form 5.

For the riprap to soil interface:

and

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Therefore, a filter layer is needed.

Try 13 mm uniformly graded fine gravel filter (gradation characteristics as illustrated in Form 3, Figure38).

For the filter to soil interface:

and

Therefore, filter to soil interface is OK.

For the riprap to filter interface:

and

Therefore, the 13 mm filter material is adequate. See Form 3, Figure 38 for soil, granular filter, and riprapgradation curves.

(b) Filter layer thickness:

Since soil gradation curve and filter layer, riprap, and bank soil are approximately parallel, use layerthickness of 200 mm.

Step 14. Edge Details. See Section 4.6.

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(a) Flank details: See Figure 32.

(b) Toe detail: See Figure 32.

Anticipated scour depth below existing channel bottom at the bank (d's) is the depth of scour(computed in step 12) minus the current bed elevation at the bank: See Figure 31.

6.7- 3.2 = 3.5 m

Rock quantity required below the existing bed:

Rq = 0.0283 d's (sin-1 θ)(T)(1.5)

where:

Rq =required riprap quantity per m of bank (m2)

θ =the bank angle with the horizontal (degrees)T =the riprap layer thickness (m)

Rq = (3.048) (2.24) (0.9144) (1.5) = 9.38 m2

A 1.83 m deep trapezoidal toe trench with side slopes of 1V:2H and 1V:1H, and a bottom width of 1.8 mcontains the necessary volume.

Figure 32 illustrates the resulting toe trench detail.

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Figure 31. Channel Cross Section for Example 2, Illustrating Flow and Potential Scour Depths

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Figure 32. Toe and Flank Details; Example 2

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The following forms may benefit from the D50 Calculation form:Archive

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Chapter 6 : HEC 11Guidelines for Other Revetments

Go to Appendix A

This chapter contains design and construction guidelines for wire-enclosed rock, preformed block, groutedrock, and concrete pavement revetments. Sample specifications for each type of revetment can be foundin Appendix A.

Figure 39 shows a revetment schematic illustrating the three typical design sections for bank and channelrevetments. Section A-A is a mid-section profile characteristic of a typical design section as well asdocumenting the revetment toe and top details. Sections B-B and C-C are flank sections documenting theupstream and downstream edge details respectively. These three section references are used to providedesign details for each of the revetments described below.


As described in Section 2.2, wire-enclosed rock (gabion) revetments consist of rectangular wire meshbaskets filled with rock. The most common types of wire-enclosed revetments are mattresses and stackedblocks. The wire cages which make up the mattresses and gabions are available from commercialmanufacturers (see Appendix B). If desired, the wire baskets can also be fabricated from available wirefencing materials.

See Section 2.2, for general performance characteristics of wire-enclosed rock revetments.

6.1.1 Mattresses

Rock and wire mattress revetments consist of flat wire baskets or units filled with rock that arelaid end to end and side to side on a prepared channel bed and/or bank. The individualmattress units are wired together to form a continuous revetment mattress.

6.1.1.1 Design Guidelines for Rock and Wire Mattresses

Components of a rock and wire mattress design include layout of a general scheme orconcept, bank and foundation preparation, mattress size and configuration, stone size, stonequality, basket or rock enclosure fabrication, edge treatment, filter design. Design guidance isprovided below in each of these areas.

General: Rock and wire mattress revetments can be constructed from commercially availablewire units as illustrated in the details of Figure 40 and Figure 41, or from available wire fencingmaterial as illustrated in Figure 42. The use of commercially available basket units is the mostcommon practice, and is also usually the least expensive approach.

Rock and wire mattress revetments can be used to protect either the channel bank (asillustrated in the sections of Figure 40) or the entire channel perimeter (Figure 41). When usedfor bank protection, rock and wire mattress revetments consist of two distinct sections: a toesection and upper bank paving (see Figure 40). As illustrated in Figure 40, a variety of toe

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designs can be used. These designs are detailed later.

Figure 39. Revetment Schematic

The vertical and longitudinal extent of the mattress should be set based on guidelines providedin Section 3.6. Emphasis in design should be placed on toe design, and filter design.

Bank and Foundation Preparation: Channel banks should be graded to a uniform slope. Thegraded surface, either on the slope or on the stream bed at the toe of slope on which the rockand wire mattress is to be constructed, should not deviate from the specified slope line by morethan 150 mm.

All blunt or sharp objects (such as rocks or tree roots) protruding from the graded surfaceshould be removed.

Large boulders near the outer edge of the toe and apron area should be removed.

Mattress Unit Size and Configuration: Individual mattress units should be a size that is easilyhandled on site. Commercially available gabion units come in standard sizes as indicated inTable 4. Manufacturer's literature indicates that alternative sizes can be manufactured whenrequired, provided that the quantities involved are of a reasonable magnitude.

The mattress should be divided into compartments so that failure of one section of the mattresswill not cause loss of the entire mattress. Compartmentalization also adds to the structuralintegrity of individual gabion units. It is recommended that diaphragms be installed at a nominal0.91 m spacing within each of the gabion units to provide the recommendedcompartmentalization (see Figure 43).

On steep slopes (greater than 3H:1V), and in environments subject to high stresses (in areasprone to high flow velocities, debris flows, ice flows, etc.), diaphragms should be spaced atminimum intervals of 0.61 m to prevent movement of the stone inside the basket (as describedin Chapter 2).

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Figure 40. Rock and Wire Mattress Configurations: (a) Mattress with Toe Apron; (b) Mattress withToe Wall; (c) Mattress with Toe Wall; and (d) Mattress of Variable Thickness (see section A-A of

Figure 39 for reference)

Figure 41. Rock and Wire Mattress Installation Covering the Entire Channel Perimeter(see section A-A of Figure 39 for reference)

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Figure 42. Typical Detail of Rock and Wire Mattress Constructed from Available Wire FencingMaterials (see section A-A of Figure 39 for reference)

Table 4. Standard Gabion SizesThickness (m) Width (m) Length (m) Wire-Mesh

Opening Size(mm x mm)

0.2290.229

1.8291.829

2.7433.658

63.5 x 82.5563.5 x 82.55

0.3050.3050.305

0.9140.9140.914

1.8292.7433.658

82.55 x 114.382.55 x 114.382.55 x 114.3

0.4570.4570.457

0.9140.9140.914

1.8292.7433.658

82.55 x 114.382.55 x 114.382.55 x 114.3

0.9140.9140.914

0.9140.9140.914

1.8292.7433.658

82.55 x 114.382.55 x 114.382.55 x 114.3

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The thickness of the mattress is determined by three factors:The erodibility of the bank soil1.

The maximum velocity of the water, and2.

The bank slope.3.

The minimum thickness required for various conditions is tabulated in Table 5. These valuesare based on observations of a large number of mattress installations which assume a fillingmaterial in the size range of 76 to 152 mm.

The mattress thickness should be at least as thick as two overlapping layers of stone.

The thickness of mattresses used as bank toe aprons should always exceed 300 mm. Thetypical range is 300 to 510 mm. The thickness of mattress revetments can vary according toneed by utilizing gabions of different depths as illustrated in Figure 40d.

Stone Size: The maximum size of stone should not exceed the thickness of individual mattressunits. The stone should be well graded within the sizes available, and 70 percent of the stone,by weight, should be slightly larger than the wire-mesh opening. For commercially availableunits, the wire-mesh opening sizes are listed in Table 4.

Common median stone sizes used in mattress designs range from 76 to 152 mm formattresses less than 0.31 m thick. For mattresses of larger thickness, rock having a mediansize up to 0.31 m is used.

Stone Quality: The stone should meet the quality requirements as specified for dumped-rockriprap given in Chapter 4.

Figure 43. Mattress ConfigurationTable 5. Criteria for Gabion Thickness

Bank Soil Type MaximumVelocity(m/sec)

Bank Slope Min. RequiredMattress

Thickness(mm)

Clays, heavycohesive soils

3.0483.962-4.877

any

< 3V:1H< 2V:1H< 2V:1H

228.6304.8

> 457.2Silts, fine sands 3.048 < 2V:1H 304.8

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Shingle withgravel

4.8776.096any

< 3V:1H< 2V:1H< 2V:1H

228.6304.8

> 457.2

Basket Fabrication: Commercially fabricated basket units are formed from galvanized steelwire mesh of triple twist hexagonal weave. The netting wire and binding wire is approximatelyNo. 13-1/2 gage. The wire for edges and corners is approximately No. 12 gage. Manufacturer'sinstructions for field assembly of basket units should be followed.

Wire mattress units may also be fabricated from available fencing materials. The wireenclosure should be formed from galvanized woven-wire fencing of No. 9 or No. 12 gagegalvanized wire. Ties and lacing wire should be No. 9 gage galvanized wire.

All wire used in the construction of the mesh rock enclosures (including tie wire) shall be zinccoated (galvanized) to ASTM A641-71A (1980); the minimum weight of the zinc coating shallbe as follows:

Nominal Diameter of Wire Minimum Coating Weight2.2 mm 214 g/m2

2.7 mm 244 g/m2

3.4 mm 244 g/m2

The adhesive of the zinc coating to the wire should be such that, when the wire is wrapped sixturns around a mandrel measuring 4 times the diameter of the wire, it does not flake or crack tosuch an extent that any zinc can be removed by rubbing with bare fingers.

Galvanized wire baskets may be safely used in fresh water and in areas where the pH of theliquid in contact with it is not greater than 10. For highly corrosive conditions such as in saltwater environments, industrial areas, polluted streams, and in soils such as muck, peat, andcinders, a polyvinyl chloride (PVC) coating must be used over the galvanizing. The PVCcoating must have a nominal thickness of 0.55 mm and shall nowhere be less than 0.38 mm. Itshall be capable of resisting deleterious effects of natural weather exposure and immersion insalt water, and shall not show any material difference in its initial characteristics with time.

Edge Treatment: The edges of rock and wire mattress revetment installations (the toe, head,and flanks) require special treatment to prevent damage from undermining. Of primary concernis toe treatment. Figure 40 illustrates several possible toe configurations. Figure 40a illustratesa toe apron, Figure 40b illustrates a toe wall, and Figure 40c illustrates the use of a toe wall incombination with an apron. If a toe apron is used, its projection should be 1.5 times theexpected maximum depth of scour in the vicinity of the revetment toe (see Section 3.6.2). Inareas where little toe scour is expected, the apron can be replaced by a single-course gabiontoe wall (see Figure 40b) , which helps to support the revetment and prevent undermining. Incases where an excessive amount of toe scour is anticipated, both an apron and a toe wall canbe used as illustrated in Figure 40c.

To provide extra strength at the revetment flanks, it is recommended that mattress units havingadditional thickness be used at the upstream and downstream edges of the revetment (seeFigure 44). It is further recommended that a thin layer of topsoil be spread over the flank unitsto form a soil layer to be seeded when the revetment installation is complete.

The head of rock and wire mattress revetments can usually be terminated at grade asillustrated in Figure 40.

Filter Design: Individual mattress units will act as a crude filter as well as a pavement unit

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when filled with overlapping layers of hand-size stones. However, it is recommended that theneed for a filter be investigated, and if necessary, a layer of permeable membrane cloth(geotextile) woven from synthetic fibers, or a 102-mm to 152-mm layer of gravel be placedbetween the silty bank and the rock and wire mattress revetment to further inhibit washout offines. For further discussion on filter materials, see Chapter 4.


Construction details for rock and wire mattresses vary with the design and purpose for whichthe protection is provided. Typical details are illustrated in Figure 40 , Figure 41 , Figure 42 ,Figure 43 , and Figure 44. Rock and wire mattress revetments may be fabricated where theyare to be placed, or at an off-site location. Fabrication at an off-site location requires that theindividual mattress units be transported to the site; in this case extreme care must be taken sothat moving and placing the baskets does not damage them by breaking or loosening strandsof wire or ties, or by removing any of the galvanizing or PVC coating. Because of the potentialfor damage to the wire enclosures, off-site fabrication is not recommended.

On-site fabrication of rock and wire mattress revetments is the most common practice. Asmentioned above, wire enclosures for mattress revetments can be purchased from commercialvendors (see Appendix B), or can be fabricated from galvanized woven fencing components.The economic advantages of commercial wire enclosure units (baskets) have almosteliminated on-site fabrication using wire fencing components except in special designsituations. Figure 42 illustrates details for a rock and wire mattress constructed from galvanizedfencing components. Figure 40 and Figure 42 illustrate installations on a channel bank. Figure41 illustrates a similar installation where the entire channel perimeter is lined.

Installation of mattress units above the water line is usually accomplished by placing individualunits on the prepared bank, lacing them together, filling them with appropriately sized rock, andthen lacing the tops to the individual units. A typical installation is illustrated in Figure 45.Where the mattress units must be placed below the water line in relatively shallow water,mattress units can be assembled at a convenient location and then be placed on the bankusing a crane as illustrated in Figure 46. For deep water installations, an efficient method oflarge-scale placement is to fabricate the mattress sections on a barge or pontoon and thenlaunch them into the water at the shore line (see Figure 47).

6.1.2 Stacked Block Gabions

Stacked block gabion revetments consist of rectangular wire baskets which are filled with stoneand stacked in a stepped-back fashion to form the revetment surface (see Figure 48). They arealso commonly used at the toe of embankment slopes as toe walls which help to support otherupper bank revetments and prevent undermining (Figure 40).

As illustrated in Figure 48 the rectangular basket or gabion units used for stackedconfigurations are more equidimensional than those typically used for mattress designs. Thatis, they typically have a square cross section. Commercially available gabions used in stackedconfigurations include those listed in Table 4 having 0.91 m widths and thickness. Othercommercially available sizes can also be used in the stacked block configurations.

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Figure 44. Flank Treatment for Rock and Wire Mattress Designs: (a) Upstream Face; (b)Downstream Face (see section B-B and C-C of Figure 39 respectively for reference)Arch

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Figure 45. Rock and Wire Revetment Mattress Installation (courtesy, Maccaferri Gabions, Inc.)

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Figure 46. Mattress Placement Underwater by Crane

Figure 47. Pontoon Placement of Wire Mattress

Conceptually, the gabion units for stacked block configurations could also be fabricated fromavailable fencing materials. However, the labor intensive nature of such an installation makes itimpractical in most cases. Therefore, only commercially available units are considered in thefollowing.

6.1.2.1 Design Guidelines for Stacked Block Gabions

Components of stacked gabion revetment design include layout of a general scheme or

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concept, unit size and configuration, edge treatment, backfill and filter considerations, andbasket or rock enclosure fabrication. Design guidelines for stone size and quality, and bankpreparation are the same as those discussed for mattress designs. Design guidelines for theremaining areas are discussed below.

General: Stacked gabion revetments are typically used instead of gabion mattress designswhen the slope to be protected is greater than 1H:1V or when the purpose of the revetment isfor flow training. They can also be used as retaining structures when space limitations prohibitbank grading to a slope suitable for other revetments. Typical design schemes include flowtraining walls, Figure 48a, and low or high retaining walls, Figure 48b and Figure 48crespectively.

Stacked gabion revetments must be based on a firm foundation. The foundation or baseelevation of the structure should be well below any anticipated scour depth. Additionally, inalluvial streams where channel bed fluctuations are common, an apron should be used asillustrated in Figure 48a and Figure 48b. Aprons are also recommended for situations wherethe estimated scour depth is uncertain.

Size and Configuration: Common commercial sizes for stacked gabions are listed in Table 4.The most common sizes used are those having widths and depths of 0.91 m. Sizes less than0.31 m thick are not practical for stacked gabion installations.

Typical design configurations include flow training walls and structural retaining walls. Theprimary function of flow training walls (Figure 48a) is to establish normal channel boundaries inrivers where erosion has created wide channel, or to realign the river when it is encroaching onan existing or proposed structure. A stepped-back wall is constructed at the desired banklocation; counterforts are installed to tie the walls to the channel bank at regular intervals asillustrated. The counterforts are installed to form a structural tie between the training wall andthe natural stream bank, and to prevent overflow from scouring a channel behind the wall.Counterforts should be spaced to eliminate the development of eddy or other flow currentsbetween the training wall and the bank which could cause further erosion of the bank. Thedead water zones created by the counterforts so spaced will encourage sediment depositionbehind the wall which will enhance the stabilizing characteristics of the wall.

Retaining walls can be designed in either a stepped-back configuration as illustrated in Figure48b and Figure 48c, or a batter configuration as illustrated in Figure 48d. Structural details andconfigurations can vary from site to site.

Gabion walls are gravity structures and their design follows standard engineering practice forretaining structures. Design procedures are available in standard soil mechanics texts as wellas in gabion manufacturer's literature.Arch

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Figure 48. Typical Stacked Block Gabion Revetment Details: (a) Training Wall with Counterforts; (b)Stepped Back Low Retaining Wall with Apron; (c) High Retaining Wall, Stepped-Back

Configuration; (d) High Retaining Wall, Batter Type

Edge Treatment: The flanks and toe of stacked block gabion revetments require specialattention. The upstream and downstream flanks of these revetments should includecounterforts, see Figure 48a. The counterforts should be placed 3.7 to 5.5 m from theupstream and downstream limits of the structure, and should extend a minimum of 3.7 m intothe bank.

The toe of the revetment should be protected by placing the base of the gabion wall at a depthbelow anticipated scour depths. In areas where it is difficult to predict the depth of expectedscour, or where channel bed fluctuations are common, it is recommended that a mattressapron be used. The minimum apron length should be equal to 1.5 times the anticipated scourdepth below the apron. This length can be increased in proportion to the level of uncertainty inpredicting the local toe scour depth.

Backfill/Filter Requirements: Standard retaining wall design requires the use of selectedbackfill behind the retaining structure to provide for drainage of the soil mass behind the wall.The permeable nature of gabion structures permits natural drainage of the supportedembankment. However, since material leaching through the gabion wall can become trappedand cause plugging, it is recommended that a granular backfill material be used, see Figure48d, The backfill should consist of a 51 to 305 mm layer of graded crushed stone backed by alayer of fine granular backfill.

Basket Fabrication: Commercially fabricated basket units are formed from galvanized steel

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wire mesh of triple twist hexagonal weave. The netting wire and binding wire specifications arethe same discussed for mattress units. Specifications for galvanizing and PVC coatings arealso the same for block designs as for mattresses. Figure 49 illustrates typical details of basketfabrication.


Construction details for gabion installations typically vary with the design and purpose for whichthe protection is being provided. Several typical design schematics were presented in Figure48 and Figure 49. Design details for a typical stepped-back design and a typical batter designare presented in Figure 50.

As with mattress designs, fabrication and filling of individual basket units can be done at thesite, or at an off-site location. The most common practice is to fabricate and fill individualgabions at the design site. The following steps outline the typical sequence used for installing astacked gabion revetment or wall:

Step 1. Prepare the revetment foundation. This includes excavation for thefoundation and revetment wall.

Step 2. Place the filter and gabion mattress (for designs which incorporate thiscomponent) on the prepared grade, then sequentially stack the gabion baskets toform the revetment system.

Step 3. Each basket is unfolded and assembled by lacing the edges togetherand the diaphragms to the sides.

Step 4. Fill the gabions to a depth of 0.31 m with stone from 100 to 300 mm indiameter. Place one connecting wire in each direction and loop it around twomeshes of the gabion wall. Repeat this operation until the gabion is filled.

Step 5. Wire adjoining gabions together by their vertical edges; stack emptygabions on the filled gabions and wire them at front and back.

Step 6. After the gabion is filled, fold the top shut and wire it to the ends, sidesand diaphragms.

Step 7. Crushed stone and granular backfill should be placed in intervals tohelp support the wall structure. It is recommended that backfill be placed atthree-course intervals.

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Figure 49. Gabion Basket Fabrication

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Figure 50. Section Details for (a) Stepped Back and (b) Battered Gabion Retaining Walls(see reference section A-A in Figure 39)

6.2 Pre-Cast Concrete Blocks

Pre-cast concrete block revetments consist of preformed sections which interlock with each other, areattached to each other, or built together to form a continuous blanket or mat. The concrete blocks whichmake up the mats differ in shape and method of articulation, but share certain common features. Thesefeatures include flexibility, rapid installation, and provisions for the establishment of vegetation within therevetment. Manufacturers of Pre-cast concrete block revetment units are listed in Appendix B.

Pre-cast concrete block designs come in a number of shapes and configurations. Figure 51, Figure 52,Figure 53, Figure 54, and Figure 55 illustrate several commercially available concrete block designs. Note:other manufacturers and designs are available.

Pre-cast block revetments are bound using a variety of techniques. In some cases the individual blocks

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are bound to rectangular sheets of filter fabric (referred to as fabric carrier). Other manufacturers use adesign which permits interlocking of individual blocks. Other units are simply butted together at the site.The most common method is to join individual blocks with wire cable or synthetic fiber rope.

See Section 2.4 for a discussion of general performance characteristics of pre-cast concrete blocks.

6.2.1 Design Guidelines for Pre-Cast Concrete Blocks

Components of a pre-cast concrete block revetment design include layout of a general schemeor concept, bank preparation, mattress and block size, slope, edge treatment, filter design, andsurface treatment. Design information is provided below in each of these areas.

General: As illustrated in Figure 51, Figure 52, Figure 53, Figure 54, and Figure 55, pre-castblock revetments are placed on the channel bank as continuous mattresses. The vertical andlongitudinal extent of the mattress should be set based on information provided in Section 3.6.Emphasis in design should be placed on toe design, edge treatment, and filter design.

Bank Preparation: Channel banks should be graded to a uniform slope. Any large boulders,roots, and debris should be removed from the bank prior to final grading. Also, holes, softareas, and large cavities should be filled. The graded surface, either on the slope or on thestream bed at the toe of the slope on which the revetment is to be constructed, should be trueto line and grade. Light compaction of the bank surface is recommended to provide a solidfoundation for the mattress.

Mattress and Block Size: The overall mattress size is dictated by the longitudinal and verticalextent required of the revetment system (see Section 3.6). Articulated block mattresses areassembled in sections prior to placement on the bank; individual mattress sections should beconstructed to a size that is easily handled on site by available construction equipment. Thesize of individual blocks is quite variable from manufacturer to manufacturer. In addition,individual manufacturers usually have several standard sizes of a particular block available.Manufacturer's literature should be consulted when selecting an appropriate block size for agiven hydraulic condition.

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Figure 51. Monoslab Revetment (a) Block Detail and (b) Revetment Detail

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Figure 52. Armorflex (a) Block Detail and (b) Revetment Configuration

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Figure 53. Petraflex (a) Block Detail and (b) Revetment Configuration (see referencesection A-A, Figure 39)

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Figure 54. Articulated Concrete Revetment (see reference section A-A, Figure 39)

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Figure 55. Tri-lock Revetment (see reference section A-A, Figure 39)

Slope: Articulated pre-cast block revetments can be used on bank slopes up to 1V:1.5H.However, an earth anchor should be used at the top of the revetment to secure the systemagainst slippage (see Figure 52 and Figure 53).

Pre-cast block revetments that are assembled by simply butting individual blocks end to end(with no physical connection) should not be used on slopes greater than 1V:3H.

Edge Treatment: The edges of pre-cast block revetments (the toe, head, and flanks) requirespecial treatment to prevent undermining. Of primary concern in the design of mattressrevetments is the toe treatment. Two toe treatments have been used: an apron design asillustrated in Figure 51 and Figure 54, and a toe trench design as illustrated in Figure 52 andFigure 53. As a minimum, toe aprons should extend 1.5 times the anticipated scour depth inthe vicinity of the bank toe (see Section 3.6.2). If a toe trench is used, the mattress shouldextend to a depth greater than the anticipated scour depth in the vicinity of the bank toe.

Two alternatives have also been used for edge treatments at the top and flanks. The edgescan be terminated at-grade (Figure 51, Figure 52, and Figure 54) or in a termination trench.Termination trenches are recommended in environments subject to significant erosion(silty/sandy soils, and high velocities), or where failure of the revetment would result insignificant economic loss. Termination trenches provide greater protection against failure fromundermining and outflanking than do at-grade terminations. However, in instances where upperbank erosion or lateral outflanking is not expected to be a problem, grade terminations may

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provide an economic advantage.

For articulated designs, earth anchors should be placed at regular intervals along the top of therevetment (see Figure 52 to Figure 53). Anchors are spaced based on soil type, mat size, andthe size of the anchors. See manufacturer's literature for recommended spacings.

Filter: Prior to installing the mats, a geotextile filter fabric should be installed on the bank toprevent bank material from leaching through the openings in the mattress structure. Although afabric filter is recommended, graded filter material can be used if it is properly designed andinstalled to prevent movement of the graded material through the protective mattress.Information on filter design is presented in Chapter 4.

Surface Treatment: The spaces between and within individual blocks located above the lowwater line should be filled with earth and seeded so that natural vegetation can be establishedon the bank (see Figure 52 and Figure 53). This treatment enhances both the structuralstability of the embankment and its aesthetic qualities.

6.2.2 Construction

Schematics of the types of pre-cast block revetments discussed above are provided in Figure51, Figure 52, Figure 53, Figure 54, and Figure 55. More detailed design sketches andinformation are available from individual manufacturers. Manufacturers also have availableinformation on construction procedures. Some manufacturers will provide on-site advice andassistance in the installation of their systems.

Articulated preformed block revetments can be installed by construction crews usingconventional construction equipment wherever a dragline or crane can be maneuvered.Construction procedures for most preformed block revetments are similar. After all sitepreparation work is completed, construction follows the following sequence:

Step 1. Excavate toe, flank and upper bank protection trenches as required.

Step 2. Place filter fabric and/or graded filter material on the preparedsubgrade.

Step 3. Individual mats are then attached to a spreader bar and lifted with acrane or backhoe for placement on the embankment slope. Mats are placed sideby side o the bank until the entire prepared surface is covered.

Step 4. Adjacent mats are secured to one another by fastening sideconnecting cables and end loops, or by pouring side connecting keys.

Step 5. Optional anchors are placed at the top and flanks of the protection asrequired.

Step 6. Backfill is then spread over the mats (and into the open cells orspaces between cells) and into the anchor trenches. Anchor trenches are thencompacted, and the general backfill should be seeded and fertilized according tolocal seasonal conditions.

Non-articulated block revetments (i.e., where the blocks are butted together instead of being

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physically attached) are constructed in a similar fashion, except that the individual blocks mustbe placed on the bank by hand, one at a time. This results in a much more labor-intensiveinstallation procedure.

6.3 Grouted Rock

Grouted rock revetment consists of rock slope-protection having voids filled with concrete grout to form amonolithic armor. See Section 2.4 for additional descriptive information and general performancecharacteristics for grouted rock. Sample specifications for components of grouted rock revetments areprovided in Appendix A.

6.3.1 Design Guidelines for Grouted Rock

Components of grouted rock riprap design include layout of a general scheme or concept, bankpreparation, bank slope, rock size and blanket thickness, rock grading, rock quality, groutquality, edge treatment, filter design, and pressure relief.

General: Grouted riprap designs are rigid monolithic bank protection schemes. Whencomplete, they form a continuous surface. A typical grouted riprap section is shown in Figure56.

Grouted riprap should extend from below the anticipated channel bed scour depth to thedesign high water level plus additional height for freeboard (see Section 3.6.2). Thelongitudinal extent of protection should be as described in Section 3.6.1.

During the design phase for a grouted riprap revetment, special attention needs to be paid toedge treatment, foundation design, and mechanisms for hydrostatic pressure relief. Each ofthese items is discussed below.

Bank and Foundation Preparation: The bank should be prepared by first clearing all treesand debris from the bank, and grading the bank surface to the desired slope. In general, thegraded surface should not deviate from the specified slope line by more than 152 mm.However, local depressions larger than this can be accommodated since initial placement offilter material and/or rock for the revetment will fill these depressions.

Since grouted riprap is rigid but not extremely strong, support by the embankment must bemaintained. To form a firm foundation, it is recommended that the bank surface be tamped orlightly compacted. Care must be taken during bank compaction to maintain a soil permeabilitysimilar to that of the natural, undisturbed bank material. The foundation for the grouted ripraprevetment should have a bearing capacity sufficient to support either the dry weight of therevetment alone, or the submerged weight of the revetment plus the weight of the water in thewedge above the revetment for design conditions, whichever is greater.

Any large boulders or debris found buried near the edges of the revetment should be removed.

Bank Slope: Bank slopes for grouted riprap revetments should not exceed 1V:1.5H.

Rock Size and Blanket Thickness: Blanket thickness and rock size requirements for groutedriprap installations are interrelated. Figure 57 illustrates a relationship between the designvelocity and the required riprap blanket thickness for grouted riprap designs. The median rocksize in the revetment should not exceed 0.67 times the blanket thickness. The largest rock

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used in the revetment should not exceed the blanket thickness.

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Figure 56. Grouted Riprap Sections: (a) Section A-A; (b) Section B-B; and (c) SectionC-C (refer to Figure 39 for section locations)

Figure 57. Required Blanket Thickness as a Function of Flow Velocity

Rock Grading: Table 6 provides guidelines for rock gradation in grouted riprap installations.Six size classes are listed.

Rock Quality: Rock used in grouted rock slope-protection is usually the same as that used inordinary rock slope-protection. However, the specifications for specific gravity and hardnessmay be lowered if necessary as the rocks are protected by the surrounding grout.

In addition, the rock used in grouted riprap installations should be free of fines in order thatpenetration of grout may be achieved.

Grout Quality and Characteristics: Grout should consist of good strength concrete using amaximum aggregate size of 19.05 mm and a slump of 76 to 102 mm. Sand mixes may be usedwhere roughness of the grout surface is unnecessary, provided sufficient cement is added togive good strength and workability.

The volume of grout required will be that necessary to provide penetration to the depths shown

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in Table 6.

The finished grout should leave face stones exposed for one-fourth to one-third their depth andthe surface of the grout should expose a matrix of coarse aggregate.

Edge Treatment: The edges of grouted rock revetments (the head, toe, and flanks) requirespecial treatment to prevent undermining. The revetment toe should extend to a depth belowanticipated scour depths or to bedrock. The toe should be designed as illustrated in Figure56a. After excavating to the desired depth, the riprap slope protection should be extended tothe bottom of the trench and grouted. The remainder of the excavated area in the toe trenchshould be filled with ungrouted riprap. The ungrouted riprap provides extra protection againstundermining at the bank toe.

To prevent outflanking of the revetment, various edge treatments are required. Recommendeddesigns for these edge treatments are illustrated in Figure 56, parts (a), (b), and (c).

Filter Design: Filters are required under all grouted riprap revetments to provide a zone ofhigh permeability to carry off seepage water and prevent damage to the overlying structurefrom uplift pressures. A 154 mm granular filter is required beneath the pavement to provide anadequate drainage zone. The filter can consist of well-graded granular material oruniformly-graded granular material with an underlying filter fabric. The filter should be designedto provide a high degree of permeability while preventing base material particles frompenetrating the filter, thus causing clogging and failure of the protective filter layer, Chapter 4contains more specific information for filter design.

Pressure Relief: Weep holes should be provided in the revetment to relieve hydrostaticpressure build-up behind the grout surface (see Figure 56a). Weeps should extend through thegrout surface to the interface with the gravel underdrain layer. Weeps should consist of 76 mmdiameter pipes having a maximum horizontal spacing of 1.8 m and a maximum vertical spacingof 3.0 m. The buried end of the weep should be covered with wire screening or a fabric filter ofa gage that will prevent passage of the gravel underlayer.

6.3.2 Construction

Construction details for grouted riprap revetments are illustrated in Figure 40. The followingconstruction procedures should be followed:

Step 1. Normal construction procedures include: bank clearing and grading ,development of foundation, placement of the rock slope protection, grouting of theinterstices, backfilling toe and flank trenches, vegetation of disturbed areas.

Step 2. The rock should be wet immediately prior to commencing the groutingoperation.

Step 3. The grout may be transported to the place of final deposit by chutes,tubes, buckets, pneumatic equipment, or any other mechanical method which willcontrol segregation and uniformity of the grout.

Step 4. Spading and rodding are necessary where penetration is achieved bygravity flow into the interstices.

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Step 5. No loads should be allowed upon the revetment until good strengthhas been developed.

6.4 Concrete Pavement

Concrete pavement revetments are cast in place, or pre-cast and set in place on a prepared slope toprovide a continuous, monolithic armor for bank protection. Cast-in-place designs are the most common ofthe two design methods. For additional descriptive information and general performance characteristics ofconcrete pavement, see Section 2.4. Sample specifications for components of concrete pavementrevetments are provided in Appendix A.

6.4.1 Design Guidelines for Concrete Pavement

Components of concrete pavement revetment design include layout of a general scheme, bankand foundation preparation, bank slope, pavement thickness, pavement reinforcement, edgetreatment, stub walls, filter design, pressure relief, and concrete quality. Each of thesecomponents is addressed below.

General: Concrete pavement designs are ridged monolithic bank protection schemes. Whencomplete they form a continuous surface. A design sketch of a typical concrete pavement isillustrated in Figure 58. As illustrated in Figure 58, typical concrete pavement revetmentconsists of the bank pavement, a toe section, a head section, cutoff or stub walls, weeps, anda filter layer.

Concrete pavements can be designed as light duty or heavy duty. The distinction between lightand heavy duty concrete pavement is in the various dimensions labeled in Table 7. Table 7,documents the labeled dimensions for both light and heavy duty concrete pavements.

As indicated in Figure 58, concrete pavements should extend vertically below the anticipatedchannel bed scour depth, and to a height equal to the design high water level plus additionalheight for freeboard (see Section 3.6.2). The longitudinal extent of protection should be asdescribed in Section 3.6.1.

An additional consideration in concrete pavement design is the surface texture. Depending onthe smoothness required for hydraulics, a float or sand finish may be specified, or if roughnessis desired, plans may call for a deformed surface obtained by grooving the surface after theinitial set.

During the design phase for concrete pavement revetment, special attention needs to be paidto toe and edge treatment, foundation design, and mechanisms for hydrostatic pressure relief.Field experience indicates that inadequacies in these areas of design are often responsible forfailures of concrete pavement revetments.

Bank and Foundation Preparation: The bank should be prepared by first clearing all treesand debris from the bank, and grading the bank surface to a slope not to exceed 1V:1.5H.

Continuity of the final graded surface is important. After grading, the surface should be true tograde, and stable with respect to slip and settlement. To form a firm foundation, it isrecommended that the bank surface be tamped or lightly compacted. Care must be takenduring bank compaction to maintain a soil permeability similar to that of the natural,

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undisturbed bank material. After compaction, the bank surface should not deviate from thespecified slope by more than several inches at any one point. This is particularly true if pre-castslabs are to be placed on the bank.

Table 6. Recommended Grading of Grouted Rock Slope ProtectionRock Sizes Classes

(Percent Larger Than Given Rock Size)

EquivalentDiameter(m)

Weight(Ton)

.9 ton .45 ton .23 ton Light Facing Cobble

1.070.840.690.530.380.300.15

1.810.9

0.450.230.090.030.01

0-550-100

95-100

0-550-100

95-100

0-550-100

95-100

0-550-10095-100

0-550-10095-100

0-595-100

Minimum Penetrationof grout (mm)

609 457 498 254 203 152

Table 7. Dimensions for Concrete SlabRevetment

ClassDIMENSION

A B C D E F G H I J K L

Light Duty 101mm 0mm 230mm 560mm 560mm 150mm 100mm 1220-1525mm 610-915mm 455mm 4750-6095mm 150mm

HeavyDuty

150mm 230mm 230mm 560mm 610mm 230mm 150mm 1220-1525mm 610-915mm 455mm 7620-9145mm 230mm

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Figure 58. Concrete Paving Detail: (a) Plan; (b) Section A-A: (c) Section B-B

The foundation for the concrete pavement revetment should have a bearing capacity sufficientto support either the dry weight of the revetment alone, or the submerged weight of therevetment plus the weight of water in the wedge above the revetment for design conditions,whichever is greater.

Bank Slope: The bank slope for concrete pavements should not exceed 1V:1.5H.

Pavement Thickness: A pavement thickness of 100 to 150 mm is recommended. Pavementthickness of up to 100 mm is referred to as a light pavement, and 150 mm paving as heavypavement.

Reinforcement: The purpose of reinforcement is to maintain the continuity of pavement byaggregate interlock even though cracks develop from shrinkage, thermal stresses, and flexuralstresses.

Reinforcement may be either mesh or bar reinforcement. Typically, No. 6-gage wire mesh isused in 100 mm slabs, and 6.3 mm rebars are used in 150 mm slabs. Both size and spacing ineach direction must be specified.

Concrete Quality: Concrete should be of good strength, and the concrete mixture shall beproportioned so as to secure a workable, finishable, durable, watertight, and wear resistantconcrete of the desired strength. Class A (AASHTO classification) proportions arerecommended. However, in some less critical design situations, Class B proportions may beused.

Edge Treatment: The edges of the concrete pavement (the toe, head, and flanks) requirespecial treatment to prevent undermining. Section A-A in Figure 58b illustrates standard headand toe designs. The head of the pavement should be tied into the bank and overlapped withsoil as illustrated to form a smooth transition from the concrete pavement to the natural bankmaterial. This minimizes scour due to the discontinuity in this area. Also, this design seals offthe filter layer from any water which overtops the revetment, thereby reducing the potential forerosion at this interface.

Section A-A also illustrates the standard toe design. The revetment toe should extend to adepth below anticipated scour or to bedrock. When this is not feasible without costlyunderwater construction, an alternative design should be considered. Several alternativedesigns are illustrated in Figure 59, including a riprap filled toe trench, a toe mattress, and asheet-pile toe wall. (Other types of toe retaining walls are also good alternatives.) In all but thelatter case, the concrete pavement should extend a minimum of 1.5 m below the channel bed;the sheet-pile toe wall can be attached to the concrete pavement above, below, or at thechannel bed level (see Section 3.6.2.2).

Section B-B [Figure 58c] illustrates flank treatment. At the upstream and downstream flanks,flank stubs are used to prevent progressive undermining at the flanks.

Stub Walls: As illustrated in Figure 58c, stub walls should be placed at regular intervals. Stubwalls provide support for the revetment at expansion joints; they also guard againstprogressive failure of the revetment.

Filter Design: Filters are required under all concrete pavement revetments to provide a zoneof high permeability to carry off seepage water and prevent damage to the overlying structurefrom uplift pressures. A 100 to 150 mm granular filter is required beneath the pavement to

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provide an adequate drainage zone. The filter can consist of well graded granular material oruniformly graded granular material underlain with an underlying filter fabric. The filter should bedesigned to provide a high degree of permeability while preventing base material particles frompenetrating the filter, thus causing clogging and failure of the protective filter layer. Chapter 4contains more specific information for filter design.

Pressure Relief: Weep holes should be provided in the revetment to relieve hydrostaticpressure build-up behind the pavement surface (see Figure 58). Weeps should extend throughthe pavement surface and into the granular underdrain or filter layer. Weeps should consist of76 mm diameter pipes having a maximum horizontal spacing of 1.8 m and a maximum verticalspacing of 3.0 m. The buried end of the weep should be covered with wire screening or filterfabric of a gage that will prevent passage of the gravel filter layer. Alternatively, a closed endpipe with horizontal slits can be used for the drain; in this case, the slits must be of a size thatwill not pass the granular filter material.

6.4.2 Construction

Design details for concrete slope pavement are illustrated in Figure 58. The followingconstruction procedures and specifications are given:

Normal construction procedures include:●

bank clearing and grading,.

development of a foundation,b.

trenching and setting forms for stubs,c.

placing the filter layer,d.

forming for and placing the concrete pavement (including any specialadaptations necessary for the revetment toe,

e.

backfilling toe trenches (if required), andf.

vegetation of disturbed areas.g.

The usual specifications for placing and curing structural concrete should apply toconcrete slope paving.

●

Subgrade should be dampened before placement of the concrete.●

Reinforcement must be supported so that it will be maintained in its proper position in thecompleted paving.

●

If the slope is too steep to allow ordinary hand finishing, a 6.4 mm thickness of mortarmay be applied immediately after the concrete has set.

●

Slabs should be laid in horizontal courses, with cold joints without filler between courses.These joints should be formed with 20 mm lumber, which should be removed and thejoint left open upon completion.

●

Vertical expansion joints should run normal to the bank at 4.6 to 9.1 m intervals. Thesejoints should be formed using joint filler.

●

Headers or forms for use during screening or rodding operations must be firm enoughand so spaced that adjustment will not be necessary during placement operations.

●

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Figure 59. Concrete Pavement Toe Details

Go to Appendix A

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Appendix A : HEC 11Suggested Specifications

Go to Appendix B

This Appendix Contains suggested specifications for:rock riprap,●

wire-enclosed rock,●

grouted rock,●

pre-cast concrete block revetments, and●

paved lining.●

These specifications are presented for the information of the designer, and should be modified asrequired for each individual design.

7.1 Riprap

7.1.1 Description

This work consists of furnishing materials and performing all work necessary to placeriprap on bottoms and side slopes of channels, or as directed by the engineer.

The types of riprap included in this specification are:

a. Rock Riprap: Riprap consists of stone dumped in place on a filter blanket orprepared slope to form a well-graded mass with a minimum of voids.b. Rubble: Rubble refers to waste construction material used as riprap. Types ofrubble include broken concrete, rock spoils, and steel furnace slag.

7.1.2 Materials

All materials shall meet the following requirements:

a. Rock Riprap: Stone used for riprap shall be hard, durable, angular in shape;resistant to weathering and to water action; free from overburden, spoil, shale andorganic material; and shall meet the gradation requirements specified. Neither breadthnor thickness of a single stone should be less than one-third its length. Roundedstone or boulders will not be accepted unless authorized by special provisions. Shaleand stone with shale seams are not acceptable. The minimum weight of the stoneshall be 2,482 kg/m3 as computed by multiplying the specific gravity(bulk-saturated-surface-dry basis, AASHTO Test T 85) times 1,000 kg/m3 .

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The sources from which the stone will be obtained shall be selected well in advance ofthe time when the stone will be required in the work. The acceptability of the stone willbe determined by service records and/or by suitable tests. If testing is required,suitable samples of stone shall be taken in the presence of the engineer at least 25days in advance of the time when the placing of riprap is expected to begin. Theapproval of some rock fragments from a particular quarry site shall not be construedas constituting the approval of all rock fragments taken from that quarry.

In the absence of service records, resistance to disintegration from the type ofexposure to which the stone will be subjected will be determined by any or all of thefollowing tests as stated in the special provisions:

When the riprap must withstand abrasive action from material transported by thestream, the abrasion test in the Los Angeles machine shall also be used. Whenthe abrasion test in the Los Angeles machine (AASHTO Test T 96) is used, thestone shall have a percentage loss of not more than 40 after 500 revolutions.

●

In locations subject to freezing or where the stone is exposed to salt water, thesulfate soundness test (AASHTO Test T 104 for ledge rock using sodiumsulfate) shall be used. Stones shall have a loss not exceeding 10 percent withthe sulfate test after 5 cycles.

●

When the freezing and thawing test (AASHTO Test 103 for ledge rockprocedure A) is used as a guide to resistance to weathering, the stone shouldhave a loss not exceeding 10 percent after 12 cycles of freezing and thawing.

●

Each load of riprap shall be reasonably well-graded from the smallest to the maximumsize specified. Stones smaller than the specified 10 percent size and spalls will not bepermitted in an amount exceeding 10 percent by weight of each load.

Control of gradation will be by visual inspection. The contractor shall provide twosamples of rock of at least 2.27 kilograms each, meeting the gradation specified. Thesample at the construction site may be a part of the finished riprap covering. The othersample shall be provided at the quarry. These samples shall be used as a frequentreference for judging the gradation of the riprap supplied. Any difference of opinionbetween the engineer and the contractor shall be resolved by dumping and checkingthe gradation of two random truck loads of stone. Mechanical equipment, a sortingsite, and labor needed to assist in checking gradation shall be provided by thecontractor at no additional cost the State.

b. Rubble: Materials used as rubble riprap shall be hard, durable, angular in shape;resistant to weathering and to water action; free from overburden, spoil, shale andorganic material; and shall meet the gradation requirements specified. Neither breadthnor thickness of a single unit should be less than one-third its length.

Extreme care must be exercised in the selection of rubble for use as riprap.

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a. General: Slopes to be protected by riprap shall be free of brush, trees, stumps, andother objectionable materials and be dressed to smooth surface. All soft or spongymaterial shall be removed to the depth shown on the plans or as directed by theengineer and replaced with approved native material. Filled areas will be compactedas specified for embankments. A toe trench as shown on the plans shall be dug andmaintained until the riprap is placed.

Protection for structured foundations shall be provided as early as the foundationconstruction permits. The area to be protected shall be cleared of waste materials andthe surf aces to be protected prepared as shown on the plans. The type of riprapspecified will be placed in accordance with these specifications as modified by thespecial provisions.

When shown on the plans, a filter blanket or filter fabric shall be placed on theprepared slope or area to be provided with foundation protection as specified in Table8 before the stone is placed.

I. Minimum Quality Standards

Fibers used in the manufacture of geotextiles shall consist of long chainsynthetic polymers, composed of at least 85% by weight polyolafins, polyesters,or polyamides.

.

Geotextiles with low resistance to ultraviolet degradation (more than 30%strength loss at 500 hours exposure ASTM D-4355) should not be exposed tosunlight for more than 7 days.

B.

Geotextiles with higher resistance to ultraviolet degradation should not beexposed for more than 30 days. NOTE: Geotextiles can be manufacturedor finished to resist degradation due to prolonged exposure to ultravioletradiation, i.e., fabrics resistant to exposure for multi-year periods (from 5to 25 years) are not uncommon.Physical Property Requirements are shown in Table 8 below:C.

Table 8. Recommended Minimum Properties for Synthetic Fabrics (Geotextiles) Used in Noncritical(1)

/Nonsevere Drainage(2), Filtration, and Erosion Control ApplicationsTest Methods* Drainage(3) Erosion Control(3)

Class A(4) Class B(5) Class A(6) Class B(7)

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Grab Strength (TF #25 Method 1) (Min. in eitherprinciple direction.)

Elongation (TF #25 method 1) (Min. in either principledirection)

Puncture Strength (TF #25 Method 4)

Burst Strength (TF #25 Method 3)

Trapezoid Tear (TF #25 Method 2)

800 N

NotSpecified

800 N

2.0E06 Pa

222 N

356 N

NotSpecified

111 N

(9.0E05 Pa)

111 N

890 N

15%

800 N

2.2E06 Pa

222 N

400 N

15%

178 N

1.0E06 Pa

(133 N)*Test methods are in accordance with procedures outlined in the FHWA Geotextile Engineering Manual(26).

II. Minimum Hydraulic Properties

a. Piping Resistance (soil retention) (8)

1. Soil with 50% or less particles by weight passing U.S. No.200 Sieve(9) ;

AOS(10) less than 0.6mm (greater than #30 U.S. Std.Sieve)

2. Soil with more than 50% particles by weight passing U.S.No. 200 Sieve(9);

AOS(10) less than 0.3mm (greater than #50 U.S. Std.Sieve)

b. Permeability

K of fabric (11) greater than K of soil

The contractor shall maintain the riprap until all work on thecontract has been completed and accepted. Maintenance shallconsist of the repair of areas where damaged by any cause.

B. Rock Riprap: Stone for riprap shall be placed on the prepared slope or area in amanner which will produce a reasonably well-graded mass of stone with the minimumpracticable percentage of voids. The entire mass of stone shall be placed so as to bein conformance with the lines, grades, and thickness shown on the plans. Riprap shallbe placed to its full course thickness at one operation and in such a manner as toavoid displacing the underlying material. Placing of riprap in layers, or by dumping intochutes, or by similar methods likely to cause segregation, will not be permitted.

The larger stones shall be well distributed and the entire mass of stone shall conformto the gradation specified by the engineer. All material going into riprap protectionshall be so placed and distributed so that there will be no large accumulations ofeither the larger or smaller sizes of stone.

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It is the intent of these specifications to produce a fairly compact riprap protection inwhich all sizes of material are placed in their proper proportions. Hand placing orrearranging of individual stones by mechanical equipment may be required to theextent necessary to secure the results specified.

Unless otherwise authorized by the engineer, the riprap protection shall be placed inconjunction with the construction of the embankment with only sufficient lag inconstruction of the riprap protection as may be necessary to allow for properconstruction of the portion of the embankment protected and to prevent mixture ofembankment and riprap. The contractor shall maintain the riprap protection untilaccepted, and any material displaced by any cause shall be replaced to the lines andgrades shown on the plans at no additional cost to the State.

When riprap and filter material are dumped under water, thickness of the layers shallbe increased as shown on the plans; and methods shall be used that will minimizesegregation.

Notes:

1.Critical applications involve the risk of loss of life, potential for significant structural damage, or whererepair costs would greatly exceed installation costs.

2. Severe applications include draining gap graded or pipable soil, high hydraulic gradients or reversing,or cyclic flow conditions.

3. All numerical values represent minimum average roll values, i.e., values measured for a sample(average of all specimen results) should meet or exceed specified values within a 2 sigma confidencelevel. These values are considerably lower than those commonly presented in manufacturers literature.

4. Class A Filtration and Drainage applications for fabrics are where installation stresses are more severethan Class B applications, i.e., very sharp angular aggregate is used, a heavy degree of compaction isspecified, or depth of trench is greater than 3 m.

5. Class B Filtration and Drainage applications are those where fabric is used with smooth gradedsurfaces having no sharp angular projections, no sharp angular aggregate is used; compactionrequirements are light, and trenches are less than 3 m in depth.

6. Class A Erosion Control applications are those where fabrics are used under conditions whereinstallation stresses are more severe than Class B, i.e., stone placement height should be less than 0.91m and stone weights should not exceed 113 kg. Field trials are required where stone placement heightexceeds 0.91 m or where stone weight exceeds 113 kg.

7. Class B Erosion Control applications are those where fabric is used in structures or under conditionswhere the fabric is protected by a sand cushion or by "zero drop height" placement of stone.

8. Design values as determined by an engineering analysis which assure compatibility between soil,hydraulic conditions, and geotextile are recommended (especially for critical/severe applications).Problem soils where the above guidelines may not apply are silts and uniform sands with 85% passingthe #100 sieve.

9. When protected soil contains particle sizes greater than #4 U.S. Std Sieve size, use only that gradationof soil passing the #4 U.S. Std. Sieve in selecting the fabric.

10. AOS determined for geotextiles according to TF #25 method 6.

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11. Permeability determined for geotextiles according to TF #25 method 5.


The quantity of riprap to be paid for, of specified thickness and extent, in place andaccepted, shall be measured by the number of cubic yards as computed from surfacemeasurements parallel to the riprap surface and thickness measured normal to theriprap surface. Riprap placed outside the specified limits will not be measured or paidfor, and the contractor may be required to remove and dispose of the excess riprapwithout cost to the State.


The quantities determined, as provided in Section 7.1.4 shall be paid for at thecontract unit price per cubic yard shown in the bid schedule, which price shall be fullcompensation for furnishing all material, tools, and labor for the preparation of thesubgrade; the placing of the riprap; and all other work incidental to finishedconstruction in accordance with these specifications.


7.2.1 Description

This work will consist of furnishing all materials and performing all work necessary toplace wire-enclosed rock on bottoms and side slopes of channels or as directed bythe engineer. Wire-enclosed rock consists of mats of baskets fabricated from wiremesh, filled with stone, connected together, and anchored to the slope. Details ofconstruction may differ depending upon the degree of exposure and the service,whether used for revetment or used as a toe protection for the other types of riprap.

7.2.2 Materials

Rock: Rock used to fill the wire units shall meet the requirements of Section7.1.2, except for size and gradation of stone. Stone used shall be well-gradedand 70 percent, by weight, shall exceed in least dimension the wire meshopening. The maximum size of stone, measured normal to the slope, shall notexceed the mattress thickness.

1.

Wire enclosures: The wire used to fabricate the mattress or block units shall beof the gage and dimensions shown on the plans.

2.

Lacing wire: Ties and lacing wire shall be No. 9 gage galvanized unlessotherwise specified.

3.

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Construction requirements shall meet those given in Section 7.1.3. Wire enclosuresegments shall be hand or machine formed to the dimensions shown on the plans.Enclosure segments shall be placed, laced, and filled to provide a uniform, dense,protective coat over the area specified.

Perimeter edges of wire-enclosed units are to be securely bound so that the jointsformed by tying the edges have approximately the same strength as the body of themesh. Wire-enclosed units shall be tied to their neighbors along all contacting edgesat left 0.31 m intervals in order to form a continuous connected structure.

Mattresses on channel side slopes should be tied to the banks by anchor stakesdriven 1.2 m into tight soil (clay) and 1.8 m into loose soil (sand). The anchor stakesshould be located at the inside corners of basket diaphragms along an upslope(highest) basket wall, so that the stakes are an integral part of the basket. The exactmaximum spacing of the stakes depends upon the configuration of the baskets;however, the following is the minimum spacing: stakes every 1.8 m along and downthe slope for slopes 1V:2.5H and steeper, and every 2.7 m along and down the slopefor slopes flatter that 1V:2.5H. Counterforts are optional with slope mattress linings.Slope mattress staking, however, is required, whether or not counterforts are used.

Channel linings should be tied to the channel banks with wire-enclosed riprapcounterforts at least every 3.7 m. Counterforts should be keyed at least 300 mm intothe existing banks with slope mattress linings and should be keyed at least 0.91 m byturning the counterfort endwise when the lining is designed to serve as a retainingwall.


The quantity of wire-enclosed riprap of specified thickness and extent in place andaccepted, shall be measured by the number of square yards obtained bymeasurements parallel to the revetment surface. Riprap placed outside the specifiedlimits will not be measured or paid for, and the contractor may be required to removeand dispose of the excess without cost to the State.


The quantities determined, as provided in Section 7.2.4 shall be paid for at thecontract unit price per square yard shown in the bid schedule, which price shall be fullcompensation for furnishing all material, tools, and 1abor for preparation of thesubgrade; placing the revetment; and all other work incidental to finished constructionin accordance with these specifications.

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7.3 Grouted Rock Riprap

7.3.1 Description

This work will consist of furnishing all materials and performing all work necessary toplace grouted rock riprap on bottoms and side slopes of channels or as directed bythe engineer. Grouted rock riprap consists of rock-slope protection having voids filledwith concrete grout to form a monolithic armor.

7.3.2 Materials

All materials shall meet the following requirements:Rock: Stone used shall meet the requirements of Section 7.1.2.●

Grout: The grout sha11 be made of good strength concrete using a maximumaggregate size of 20 mm and a slump of 80-100 mm.

●


Construction requirements shall meet those given in Section 7.1.3, and shall meet thefollowing additional requirements:

The rock shall be wet immediately prior to commencing the grouting operation.●

The rock to be grouted shall be basically free of fines in order that penetration ofgrout be achieved.

●

The ends shall be protected by tying them into solid rock or forming smoothtransitions with embankment subjected to lower velocities.

●

The grouted rock shall be founded on solid rock or below the depth of possiblescour.

●

A foundation treatment shall be required if the foundation is not reasonably dry.●

Weep holes shall be provided in the blanket to relieve any hydrostatic pressurebehind the blanket.

●

The finished grout shall leave face stones exposed for one-fourth to one-thirdtheir depth and the surface of the grout shall expose a matrix of coarseaggregate.

●

The grout shall be transported to the place of final deposit by use of chutes,tubes, buckets, pneumatic equipment, or any other mechanical method whichwill control segregation and uniformity of the grout.

●

Spading and rodding shall be required where penetration is achieved by gravityflow into the interstices.

●

No loads shall be allowed upon the revetment until good strength has beendeveloped.

●

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The quantity of grouted rock riprap to be paid for, of specified thickness and extent, inplace and accepted, shall be measured by the number of cubic meters computed fromsurface measurements parallel to the riprap surface, and thickness measured normalto the riprap surface. Riprap placed outside the specified limits will not be measuredor paid for, and the contractor may be required to remove and dispose of the excessriprap without cost to the State.


The quantities determined, as provided in Section 7.3.4. shall be paid for at thecontract unit price per cubic meter shown in the bid schedule, which price shall be fullcompensation for furnishing all material, tools, and labor for preparation of thesubgrade; placing the stone; grouting the stone; and all other work incidental tofinished construction in accordance with these specifications.

7.4 Pre-Cast Concrete Blocks

7.4.1 Description

This work consists of furnishing materials and performing all work necessary to placepre-cast concrete block revetment on bottoms and side slopes of channels or asdirected by the engineer.

The types of pre-cast concrete blocks included in this specification are:Cellular pre-cast concrete blocks. Cellular blocks which interlock with each otherin some manner when placed on the embankment slope, and allow vegetationto grow through the blocks.

●

Articulated concrete blocks. Concrete blocks held together by steel rods orcables and placed on the embankment slope

●

7.4.2 Materials

All materials shall meet the following requirements:

a. Cellular Pre-cast Concrete Blocks:Concrete: The concrete shall have a minimum compressive strength of 2.75E07Pa in 28 days. Portland cement shall conform to ASTM C 150, Type I, II or V,depending on soil conditions. Aggregates shall conform to ASTM C 33 and beminus 10 mm. Mixing water shall be fresh, clean, and potable. In freeze-thawareas, air entrapment of 5-1/2% to 8-1/2% shall be provided. Water reducing

●

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admixtures and/or super-plasticizers are permitted and shall conform to ASTM C494.Anchors : Anchors shall be corrosive-resistant and have provisions for attachingto the cellular mat.

●

Filter: The cellular pre-cast concrete block revetment shall have filter blanket ofgravel or fabric placed underneath the revetment. The filter shall meet therequirements given in Chapter 4.

●

All materials shall conform to the specifications for concrete masonry inStandard Specifications for Highway Bridges (30).

b. Articulated Pre-cast Blocks:Concrete: The concrete used for fabrication of the blocks shall be Class A, using7.8 sacks per cubic meter.

●

Reinforcement: The wire mesh shall be attached to the bar reinforcement andthe bar steel shall be in the indicated position shown on the plans.The wire mesh shall be 18 gage wire and the bar steel shall be 13 mm diameter.The longitudinal cable or rod linking the blocks shall be 20 mm diameter steel.

●

Anchors : Anchors shall be corrosive-resistant and have provisions for attachingto the articulated mat.

●

Filter : The articulated pre-cast concrete block revetment shall have a filterblanket of gravel or plastic placed underneath the revetment. The filter shallmeet the requirements given in Chapter 4.

●


Construction requirements shall meet those given in Section 7.1.3, and shall meet thefollowing requirements:

For cellular block revetment: All vegetation and debris shall be removed from the embankment.●

The slope shall be graded as evenly as possible.●

An anchor trench shall be dug at the top of slope to secure the mat system onthe slope.

●

A toe trench shall be dug at the bottom of the installation.●

A mat anchoring system shall be installed.●

A woven or non-woven geotextile filter fabric shall be placed on the gradedslope (if the revetment does not come with a carrier fabric).

●

The mats shall be attached to a spreader bar and lifted with a crane to place onthe embankment slope.

●

Mats shall be anchored by lapping at least 0.31 m of the mat in the anchortrench and fastening the cable loops to helix anchors that are driven into thetrench. A minimum of two anchors per mat is required.

●

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Adjacent mats shall be secured to each other by fastening the protruding cablestogether along each side of the revetment mats.

●

The anchor trenches shall be back-field and compacted until flush with the topof the mats. The slope shall be back-field with soil, fertilizer and seed.

●

The following are construction details for articulated concrete block revetment:The submerged bank shall be shaped prior to placement of the articulatedconcrete revetment.

●

The blocks shall be placed together on a launching barge that is anchored overthe underwater bank. Measuring parallel to the bank, a mattress up to 43 mwide shall be assembled by placing the blocks side by side on the launchingbarge and joining them with corrosion-resistant wire and clamps.

●

The completed mattress shall be moved off the barge and sunk in place on theunderwater bank by attaching the mattress to the bank and moving the bargetowards the middle of the stream.

●

The blocks shall be in alignment parallel to the toe of slope, and, if theembankment material is granular, the interstices between the blocks shall befilled with soil and seeded.

●

Revetment shall be placed during the low-water season usually betweenmid-July and mid-December

●

All construction shall conform to the specifications for concrete masonry in StandardSpecifications for Highway Bridges (30).


The quantity of pre-cast concrete block revetment to be paid for, of specified thicknessand extent , in place and accepted, shall be measured by the number of square yardsas computed from surface measurements parallel to the revetment surface.Revetment placed outside the specified limits will not be measured or paid for, and thecontractor may be required to remove and dispose of the excess revetment withoutcost to the State.


The quantities determined, as provided in Section 7.4.4 shall be paid for at thecontract unit price per square meter shown in the bid schedule, which price shall befull compensation for furnishing all material, tools, and labor for preparation of thesubgrade; placing the revetment; and all other work incidental to finished constructionin accordance with these specifications.

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7.5 Paved Lining

7.5.1 Description

This work will consist of furnishing all materials and performing all work necessary toplace concrete pavement revetment on bottoms and side slopes of channels or asdirected by the engineer. Concrete pavement revetments are cast in place on aprepared slope to provide the necessary bank protection.

7.5.2 Materials

All materials shall meet the following requirements:Concrete: The concrete shall be of good strength. Class A proportions with sixsacks is required.

●

Reinforcement: The reinforcement shall be 60 mm rebars in 150 mm slabs. Thespacing in each direction is specified on the plans.

●

Filter: Concrete pavement shall have a filter blanket placed underneath therevetment. The filter shall meet the requirements given in Chapter 4.

●

All materials shall conform to the specifications for concrete masonry in StandardSpecifications for Highway Bridges (30).


Construction requirements shall meet those given in Section 7.1.3, and shall meet thefollowing requirements:

The bank shall be well-compacted, true to grade and stable to maintaincontinuity: 0.15 m tolerance is allowed.

●

Subgrade shall be dampened before placement of the concrete.●

Concrete slabs shall be cast in place on the prepared slope.●

Reinforcement shall be supported so that it will be maintained in its properposition in the completed paving.

●

The slabs shall be laid in horizontal courses, and successive courses shallbreak joints with the preceding one.

●

Horizontal joints shall be normal to the slope and shall be cold joints withoutfiller. The joints extending up the slope shall be formed with 20 mm lumber,which shall be removed and the joint left open.

●

Expansion joints shall be filled with joint filler.●

A deformed surface shall be required as shown on the plans.●

Headers or forms for use during screening or rodding operations shall be firm●

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enough and so spaced that adjustment will not be necessary during placementoperations.A filter material shall be placed under the concrete slope pavement. The filtershall meet the requirements given in Chapter 4.

●

Weep holes shall be provided to assure drainage of the bank. Weep holes shallbe placed where shown on the plans.

●

The toe of slope pavement shall have a cutoff or stub wall.●

All construction shall conform to the specifications for concrete masonry in StandardSpecifications for Highway Bridges


The quantity of concrete pavement to be paid for, of specified thickness and extent, inplace and accepted, shall be measured by the number of square meters computedfrom surface measurements parallel to the riprap surface. Concrete pavement placedoutside the specified limits will not be measured or paid for, and the contractor may berequired to remove and dispose of the excess pavement without cost to the state.


The quantities determined, as provided in Section 7.5.4. shall be paid for at thecontract unit price per square meter shown in the bid schedule, which price shall befull compensation for furnishing all material, tools, and labor for preparation of thesubgrade; placing of slabs; and all other work incidental to finished construction inaccordance with these specifications.

Go to Appendix B

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Appendix B : HEC 11Stream Bank Protection Products and Manufacturers

Go to Appendix C

This Appendix Contains a listing of manufacturers of various stream bank protection productsrelated to riprap and related revetments. The list is organized by product type. Although anattempt was made to identify as many commercial products as possible, the list is notexhaustive. The intent is to provide a representative sample of available products, and does notin any way represent an endorsement of specific products by this agency.

8.1 Gabions

Company AddressBekaert Gabions 4930 Energy Way

Reno, NV 89502

Maccaferri Gabions, Inc RR#2, Box 43AWilliamsport, MD 21795

Terra Aqua Inc. 4930 Energy WayP. O. Box 7546Reno, NV 89510

8.2 Cellular Blocks

Company AddressARMORTEC Incorporated Suite 1990 Peachtree

Corners PlazaNorcross/Atlanta, GA 30071

ERCO Systems, Inc. P. O. Box 4133New Orleans, LA 70178

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Erosion Control Systems, Inc. 3349 Ridgelake Dr.Suite 101B. Metairie, LA 70002

Grass Pavers, Ltd. 3807 Crooks RoadRoyal Oak, MI 48073

Kennross-Naue Canada, Ltd. 320 Alameda DrivePalm Springs, FL 33461

Louisiana Industries P. O. Box 5396Bossier City, LA 71171

PETRAFLEX Inc. P. O. Box 599Channelview, TX 77530

8.3 Bulkheads

Company AddressALCOA Marine Corporation 8235 Pen Randal Place

Upper Marlboro, MD 20870

ARMCO Steel Corporation 419 Chanin Bldg.815 Connecticut Ave., NWWashington, DC 20006

GAF Corporation 140 W. 51st St.New York, NY 10020

Kaiser Aluminum 300 Lakeside Dr.Oakland, CA 94643

Spidel Foundations Harborand Marine Corporation

1055 North Shore Dr.Benton Harbor, MI 49022

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8.4 Filter Fabrics

Company Address

Advance Construction Specialties Company P.O. Box 17212Memphis, TN 38117

American Excelsior Company P.O. Box 249Sheboygan, WI 5308

Carthage Mills, Inc. 124 W. 66th St.Cincinnati, OH 45216

Celanese Fibers Marketing Company 1211 Avenue of the AmericasNew York, NY 10036

DuPont 1007 Market St.Wilmington, DE 19898

Gulf States Paper Corporation P. O. Box 3199Tuscaloosa, AL 35401

Johns-Manville Ken-Caryl RanchP. O. Box 5108Denver, CO 80217

Kennross-Naue Canada, Ltd. 320 Alameda DrivePalm Springs, FL 33461

Koch Brothers, Inc. 35 Osage AvenueKansas City, KS 66105

Menardi-Southern P. O. Box 12454Houston, TX 77012

Monsanto Textiles Company 800 N. Lindbergh Blvd.St. Louis, MO 63166

Ozite Corporation 1755 Butterfield Rd.Libertyville, IL 60048

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United States Textures Sales Corporation 4229 Jeffrey DriveBaton Rouge, LA 70816

Go to Appendix C

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Appendix C : HEC 11Design Charts and Forms

Go to Appendix D

The charts, tables, and forms in this appendix have been modified for viewing and printing purposes

ChartsTablesForms

List of ChartsChart 1. Riprap Size RelationshipChart 2. Correction Factor for Riprap SizeChart 3. Bank Angle Correction Factor (K1) NomographChart 4. Angle of Repose of Riprap in Terms of Mean Size and Shape of StoneChart 5. Conversion from Equivalent D50 in Meters to W50 in KgChart 6. Nomograph of Deepwater Significant Wave Height Prediction Curves (modified from reference 29)Chart 7. Hudson Relationship for Riprap Size Required to Resist Wave ErosionChart 8. Wave Run-Up on Smooth, Impermeable Slopes (modified from reference 29)

TablesTable 9. Correction for Wave Run-Up

FormsForm 1. Riprap Size-Particle ErosionForm 2. Riprap Size-Wave ErosionForm 3. Material GradationForm 4. Roughness EvaluationForm 5. Filter Design

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Appendix D : HEC 11Riprap Design Relationship Development

Go to Table of Contents

This appendix presents the development of the velocity based riprap design relationship usedin this version of HEC-11. The relationship is based on shear stress theory, yet in its final formuses flow velocity and depth as its controlling parameters. In the development of therelationship, the basic relationship is presented, followed by a discussion of its calibration, andconversion to a velocity based procedure. The recommended procedure is then compared withpreviously developed riprap design relationships.

10.1 Basic Relationship

Two methods or approaches historically have been used to evaluate a materials resistance toparticle erosion.

Permissible Velocity Approach●

Permissible Tractive Force or Sheer Stress●

Permissible tractive force methods are generally considered to be more academicallycorrect.However, critical velocity approaches are more rapidly embraced by the engineeringcommunity. Therefore, a design relationship for riprap design that is rooted in tractive forcetheory yet has velocity as its primary design parameter is needed.

The tractive force (boundary shear stress) approach focuses on stresses developed at theinterface between the flowing water and the material forming the channel boundary. By Chow'sdefinition, permissible tractive force is the maximum unit tractive force that will not causeserious erosion of channel bed material from a level channel bed. The basic premise underlyingriprap design based on tractive force theory is that the flow induced tractive force should notexceed the permissible or critical shear stress of the riprap. The average tractive force or shearstress (So) exerted by the flowing water on the channel boundary is equal to:

τo = γRS where:

γ = the unit weight of water ;R = the hydraulic radius; andS = the energy grade line slope.

(15)

The riprap materials resistance to movement (its critical shear stress, (τc) is defined by thefollowing relationship the form of which was first proposed by Shields (2):

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τc=K1 SP (γs -γ) D50

where:

SP = the Shields parameter;γs = the unit weight of the riprap material;γ = the unit weight of water;D50 = the median riprap particle size; andK1 is defined as:

(16)

K1 = [1-(sin2θ /sin2φ)]0.5

where:

θ = the bank angle with the horizontal; andφ = the riprap material's angle of repose.

(17)

The ratio of the critical shear stress exerted by the flow field given in Equation 16 and the riprapmaterial's average tractive force as given in Equation 15 is defined as the stability factor. Aslong as the stability factor is greater than 1, the critical shear stress of the material is greaterthan the flow induced tractive stress, and the material is considered stable.

Dividing Equation 16 by Equation 15, rearranging terms, and replacing the hydraulic radius (R)with the average flow depth (davg) yields the following relationship:

D50 / davg = (SF/SP) [S / K1 / (Ss - 1)]

where:

SF = the stability factorSs = the specific gravity of the rock riprap.

(18)

Equation 18 represents the basic form of the tractive stress relationship. In this form, themedian riprap size is primarily a function of flow depth and slope.

10.2 Design Relationship Calibration

Calibration of the design relationship in Equation 17 was accomplished using field datacollected during the early 1980's by Mr. James Blodgett of the U.S. Geological survey (3). Mr.Blodgett evaluated riprap performance at 39 sites. At each site various hydraulic and geometricparameters were also determined. The data tabulated for each site is included in Table 10. Ofthe 39 sites tabulated, only those indicating no damage or particle erosion were used. Also,several sites were eliminated due to a lack of complete data. The sites used in the analysisincluded sites 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 22, 23, 24, 26, 27, 28, 30,32, 33, 34, 35, 36, and 37. Of the 30 sites evaluated, 8 were unstable (exhibited particleerosion), and 23 were stable (no damage). Channel cross sections for each of the sites used inthe analysis are presented in the data section at the end of this appendix.

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The data tabulated in Table 10 illustrate the hydraulic characteristics of the channel reachesevaluated. Water surface slopes ranged from 0.00006 to 0.0162; maximum flow depths rangedfrom 1.46 m to 14.8 m; average channel velocities ranged from 0.73 m/s to 3.81 m/s;discharges ranged from 36.3 m3/s to 2,180 m3/s; and the median (D50) bank material sizeranged from 0.15 m to 0.70 m. Channel geometries for these sections ranged from symmetricto severely skewed. In addition, each of the sites evaluated was in a reach exhibiting uniform,gradually varied flow conditions.

The data analysis consisted of compiling and plotting the cross section data (X-Y coordinatepoints), evaluating the data for correctness and consistency, computing the necessaryhydraulic parameters from the data at each site, and then plotting several of the terms fromEquation 17 to evaluate the constants SF and SP. During the analysis, it was determined thatthe bank angle reported in Table 10 was in error at several sites. The bank angle was correctedin the data section; the original values were left unchanged in Table 10.

Click here to view Table 10. Site data

The focus of the analysis was to evaluate the variables SP and SF. The field data are plotted inFigure 60 as D50 /davg vs. S/K1/(Ss -1). Stable sites are plotted as squares, and unstable sitesas blackened squares. The numbers beside the plotted points are site numbers. The linessuperimposed on the data represent various combinations of SF and SP; the slope of theselines equals SF/SP.The data used to build Figure 60 are documented in Table 12.

The data plotted in Figure 60 support the use of a Shields parameter (SP) of 0.047, and astability factor ranging from 1 to 2. Five of the eight unstable sites fall below the linerepresenting a stability factor of 1. The remaining three sites plot between stability factors of 1.5and 2.0. Sites 6 and 8 were located at or just downstream of sharp bends, suggesting that theymay have been exposed to rather severe hydraulic conditions, thus justifying the higher plottingposition with respect to stability factor. No explanation is apparent for site 24.

The data in Figure 60 is limited. However, it does provide some information upon whichguidelines for the selection of stability factors can be based. Table 11 presents guidelines forthe selection of an appropriate stability factor. The guidelines in Table 11 are based in part onthe data in Figure 60, and in part on a comparison with other riprap design relationships (to bepresented in a later section).

Table 11. Criteria for Selection of Stability FactorsCondition Stability Factor Range

Uniform flow; Straight or mildly curving reach (curve radius/channel width > 30);Impact from wave action and floating debris is minimal; Little or no uncertainty indesign parameters.

1.0-1.2

Gradually varying flow; Moderate bend curvature (30 > curve radius/channelwidth > 10); Impact from waves or floating debris moderate.

1.3-1.6

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Approaching rapidly varying flow; Sharp bend curvature (10 > curveradius/channel width); Significant impact potential from floating debris and/or ice;Significant wind and/or boat generated waves 0.31 - 0.60 m; High flowturbulence; Significant uncertainty in design parameters.

1.6-2.0

Figure 60. Riprap Design Calibration

Click here to view Table 12. Riprap Relationship Calibration Data

10.3 Conversion to a Velocity Based Procedure

As mentioned above, the engineering community is more comfortable with a velocity basedrelationship than one based on channel slope as given in Equation 18. Assuming uniform flowconditions, Equation 18 can be transformed to a velocity based relationship using Manning'sequation to perform the transformation.

Manning's equation can be expressed as:S = [(V n)/(R 0.67)] 2

where:

V = average channel velocity; andn = Manning's roughness coefficient.

(19)

Manning's roughness coefficient, 'n', in Equation 19 can be related to particle size as given in

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Equation 20. Equation 20 was developed by Anderson and others (4). An equation of this formwas first proposed by Strickler in 1923 (5). The relationship has been utilized in studies ofroughness by a number of other investigators including Norman (6), and Maynord (7).

n = 0.0482 D500.167 (20)

Substituting Equation 20 into Equation 19 and replacing the hydraulic radius, R, with theaverage depth, davg, yields the following relationship for the energy slope:

S = (V2 D500.333)/(430.4 davg1.333) (21)

Substituting Equation 21 into Equation 18 and assuming a Shields parameter and stabilityfactor of 0.047 and 1.2 respectively, and specific gravity of riprap of 2.65, results in the finaldesign relationship given in Equation 22. A correction factor (Cs) for riprap materials havingspecific gravity's other than 2.65 is given in Equation 23 A correction factor (Cf ) for stabilityfactors other than 1.2 is given in Equation 24. The coefficient derived from Equation 23 andEquation 24 are multiplied times the D50 riprap size resulting from equation Equation 22.

D50 = 0.007 V3 /(davg0.5(K11.5)

where:

V=average section velocity in the main flow channel m/s);davg =the average cross section depth in the main flow channel (m);andK 1 =the bank slope correction term.

(22)

Cfs = 2.12 / (Ss - 1)1.5 (23)Cf = (SF/1.2)1.5 (24)

10.4 Comparison with Other Methods

Figure 61 and Figure 62 illustrate a comparison of several velocity based riprap designmethods. Included in the comparison are methods recommended by the California Division ofHighways, Bureau of Public Roads, HEC-11 (1967 version), U.S. Bureau of Reclamation, theU.S. Army Corps of Engineers, and Blodgett and McConaughy (8). Superimposed on thesecurves is the relationship presented in Equation 22. Equation 22 is plotted assuming anaverage flow depth of 3.0 m, and stability factors as indicated. Figure 62 shows the samecomparison illustrating the effect of the flow depth in Equation 22.

Figure 61 and Figure 62 also illustrate that the relationship of Equation 22 falls within the rangeof relationships previously developed. However, it is more flexible than the others since it isbased on flow depth as well as velocity.

Figure 63 presents a comparison of the relationship given in Equation 22 and the riprap designrelationship of HEC-15. Note that at a stability factor of 1, Equation 22 and the design

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relationship HEC-15 differ by only a small amount.

Figure 61. Comparison of Procedures for Estimating Stone Size on Channel Bank Basedon Permissible Velocities (adapted from appendix A of HEC-11, Searcy, 1967)Arch

ived


Figure 62. Comparison of Procedures for Estimating Stone Size on Channel Bank Basedon Permissible Velocities: Effect of Stability Factor Illustrated (adapted from National

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Figure 63. Comparison of Procedures for Estimating Stone Size on Channel Bank Basedon Permissible Velocities: Effect of Flow Depth Illustrated (adapted from National

Engineering Handbook)

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List of Tables for HEC 11-Design of Riprap Revetment (Metric)


Table 1. Guidelines for the Selection of Stability Factors

Table 2. Rock Riprap Gradation Limits

Table 3. Riprap Gradation Classes

Table 4. Standard Gabion Sizes

Table 5. Criteria for Gabion Thickness

Table 6. Recommended Grading of Grouted Rock Slope Protection

Table 7. Dimensions for Concrete Slab

Table 8. Recommended Minimum Properties for Synthetic Fabrics

Table 9. Correction for Wave Run-Up

Table 10. Site Data

Table 11. Criteria for Selection of Stability Factors

Table 12. Riprap Relationship Calibration Data


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Preface


ForwardThis implementation package represents major revisions to the 1967 edition of HydraulicEngineering Circular No. 11, "use of Riprap for Bank Protection." The manual has beenexpanded into a comprehensive design publication which includes recent research findings andrevised procedures. The information in the manual should be of interest to the State andFederal Hydraulic Engineers and others responsible for the design of riprap. The manual hasbeen adopted as HEC-11 in the Hydraulic Engineering Circular Series.

Copies of the manual are being distributed to the Federal Highway Administration and Regionaland Division offices and to each state highway agency. Additional copies of the report can beobtained from the National Technical Information Service, 5280 Port Royal Road, Springfield,Virginia 22161.

Thomas O. Willet, DirectorOffice of Engineering

Stanely R. Byington, Director Office of Implementation

NoticeThis document is disseminated under the sponsorship of the Department of Transportation inthe interest of information exchange. The United States Government assumes no liability forthe contents or the use thereof.

The contents of this report reflect the views of the authors, who are responsible for the factsand the accuracy of the data presented herein. The contents do not necessarily reflect thepolicy of the Department of Transportation.

This report does not constitute a standard, specification, or regulation. The United StatesGovernment does not endorse products or manufacturers. Trade or manufacturers' namesappear herein only because they are considered essential to the objective of this document.


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1. Report No.

FHWA-IP-89-016HEC-11

2. GovernmentAccession No.

3. Recipient's Catalog No.

4. Title and Subtitle

DESIGN OF RIPRAP REVETMENT

5. Report Date

March 19896. Performing Organization Report No.

7. Author(s)

Scott A. Brown, Eric S. Clyde

8. Performing Organization Report No.

9. Performing Organization Name and Address

Surton Corporation2190 Fox Mill RoadHerndon, VA 22071

10. Work Unit No. (TRAIS)

3D9C003311. Contract or Grant No.

DTFH61-85-C-0012312. Sponsoring Agency Name and Address

Office of Implementation, HRT-10Federal Highway Administration6200 Georgetown PikeMcLean, VA 22101

13. Type of Report and Period Covered

FINAL REPORTMar. 1986-Sept. 1988

14. Sponsoring Agency Code

15. Supplementary Notes

Project manager: Thomas KrylowskiTechnical assistants: Phillip L. Thompson, Dennis L. Richards, J. Sterling Jones16. Abstract

This revised version of Hydraulic Engineering Circular No. 11 (HEC-11), represents majorrevisions to the earlier (1967) edition of HEC-11. Recent research findings and reviseddesign procedures have been incorporated. The manual has been expanded into acomprehensive design publication. The revised manual includes discussions onrecognizing erosion potential, erosion mechanisms and riprap failure modes, riprap typesincluding rock riprap, rubble riprap, gabions, preformed blocks, grouted rock, and pavedlinings. Design concepts included are: design discharge, flow types, channel geometry,flow resistance, extent of protection, and toe depth. Detailed design guidelines arepresented for rock riprap, and design procedures are summarized in charts and examples.Design guidance is also presented for wire-enclosed rock (gabions), precast concreteblocks, and concrete paved linings.17. Key Words

Riprap, Revetments, Bank Protection, Gabions,Grouted Riprap, Riprap Design, Pre-cast ConcreteRiprap, Paved Linings.

18. Distribution Statement

This document is available to thepublic through the National TechnicalInformation Service, Springfield, VA22161

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19. Security Classif. (of thisreport)

Unclassified

20. Security Classif.(of this page)

Unclassified

21. No. of Pages

169

22. Price


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METRIC (SI*) CONVERSION FACTORSApproximate Conversions to SI Units

Symbol When You Know Multiply by To Find Symbol

Length

inftydmi

inchesfeetyardsmiles

2.540.30480.9141.61

millimetresmetresmetreskilometres

mmmmkm

Area

in2

ft2yd2

mi2ac

square inchessquare feetsquare yardssquare milesacres

645.20.09290.8362.590.395

millimetres squaredmetres squaredmetres squaredkilometres squaredhectares

mm2

m2

m2

km2ha

Mass Weight

ozlbT

ouncespoundsshort tons (2000 lb)

28.350.4540.907

gramskilogramsmegagrams

gkgMg

Volume

fl ozgalft3yd3

fluid ouncesgallonscubic feetcubic yards

29.573.7850.03280.0765

millilitreslitresmetres cubedmetres cubed

mLLm3

m3

Temperature (exact) oF Farhrenheit

temperature5/9 (aftersubtracting 32)

Celsiustemperture

oC

*SI is the Symbol for the International System of Measurements

Approximate Conversions to SI UnitsSymbol When You Know Multiply by To Find Symbol

Length mmmmkm

millimetresmetresmetreskilometres

0.0393.281.090.621

inchesfeetyardsmiles

inftydmi

Area mm2

m2

km2ha

millimetres squaredmetres squaredkilometres squaredhectares

0.001610.7640.392.53

square inchessquare feetsquare milesacres

in2

ft2mi2ac

Mass Weight gkgMg

gramskilogramsmegagrams (1000 kg)

0.03532.2051.103

ouncespoundsshort tones

ozlbT

Volume mLLm3

m3

millilitreslitresmetres cubedmetres cubed

0.0340.26435.3151.308

fluid ouncesgallonscubic feetcubic yards

fl ozgalft3yd3

Temerature (exact) oC Celsius

temperture9/5 (thenadd 32)

Farhrenheittemperature

oF

These factors conform to the requirement of FHWA Order 5190.1A


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Table 10. Site Data (reference 6, table 7)Site Measurement

NumberD50(ft)

SpecificGravity

Gs

Date offlood orsurvey

Correspondingdischarge, Q

(ft3/s)

WaterSurfaceSlope

sW

Depthmax.dm

SideSlope

z

AreaA

(ft2)

Velocity Shear PerformanceMeanVa

(ft/s)

MaxVm

(ft/s)

Sacramento River:

Princeton,CA 1 0.48 2.95 2/17/83 71,200 0.00091 48.7 1.3:1 12,700 5.61 7.97 2.77 No DamageCulusa, CA. 2 .67 2.77 12/22/81 40,600 .00006 47.0 1.9:1 10,300 3.93 6.17 .176 No Damage

Truckee River:

Reno, NV. 3 2.1 6/14/83 6,550 .00625 11.0 1.5:1 780 8.40 12.95 4.29 No Damage

3/13/83 7,230

4 12/20/81 8,690 .0089 13.8 946 9.19 -- 7.66 Particle Erosion

Sparks, NV 5 .71 2.68 5/27/82 3,880 .0022 12.1 1.8:1 744 5.22 8.17 1.66 No Damage 6 6/15/83 5,850 .00219 16.5 1.8:1 994 5.89 7.97 2.25 Particle Erosion

7 12/20/81 8,670 .0055 17.2 1.8:1 1,420 6.10/ -- 5.90 Particle Erosion

Pinole Creek @ Pinole, CA

cross sec.3 8 .55 2.85 1/03/82 2,250 .0049 7.3 2:1 293 7.68 -- 2.23 Particle Erosioncross sec.

0.49 2.3 2.80 1/03/82 2,250 .0172 6.4 2.1:1 212 10.6 -- 6.87 No Damage

DonnerCreek @

Truckee, Ca

10 .68 6/13/83 613 .0062 5.6 2.1:1 112 4.63 7.43 2.52 No Damage

E.F. CarsonRiver, near

Markleeville,CA.

11 2.0 2.36 6/16/83 2,150 .01224 8.5 1.5:1 260 8.27 13.59 6.49 No Damage

Site MeasurementNumber

D50(ft)

SpecificGravity

Gs



(ft3/s)

WaterSurfaceSlope

sw

Depthmax.

d(ftm)

SideSlope

z

AreaA

(ft2)

Velocity Shear(lb/ft2)

PerformanceMeanVa

(ft/s)

MaxVm(ft/s)

W. Walker River near Coleville, NV:

@ #2 12 1.4 6/11/82 1,450 .0181 6.4 1.3:1 146 9.93 15.91 7.71 No Damage

@ #3 13 .8 2.61 6/10/82 1,280 .01636 4.8 1.5:1 140 9.14 16.69 4.90 ParticleDamage

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RussianRiver nearCloverdale,

CA.

1415

.69 2.78 1/13/8312/31/81

28,8006,970

.00312.0018

12.39.7

2.1:1 6,8331.140

4.226.11

--9.46

2.391.09

No DamageNo Damage

Cosumnes River @ Dillard Rd. near Sloughhouse,CA:

@ #1 16 .78 2.79 3/13/83 26,100 .00073 24.6 2.3:1 9,975 2.62 -- 1.12 No Damage 17 -- -- 12/22/82 18,800 .00076 20.4 -- 7,301 2.52 -- .97 No Damage

@ #2 18 .7 -- 3/13/83 26,100 .00073 24.5 1.6:1 6,750 3.87 -- 1.09 Translat. slide 19 .7 -- 12/22/82 18,800 .00076 20.5 -- 5,360 3.51 11 .97 Translat Slide

@ #3 20 .64 -- 3/13/83 26,100 .00073 31.8 1.8:1 6,400 4.08 -- 1.45 Slump 21 -- -- 12/22/82 18,800 .00076 27.8 -- 5,070 3.71 -- 1.32 Slump

Rillito Cr. @T-100, AZ.

(cross section1)

22 .84 2.74 10/03/83 29,000 .0162 12.1 2:1 2,790 10.4 -- 12.2 No Damage

above SPRR(cross section

3):

23 .51 2.69

10/03/83 29,000

.0038 12.5 2.5:1 3,870 7.49

-- 2.96

ParticleErosion

Santa Cruz R@ I-19

(cross section3)

24 .65 2.71 10/03/83 45,000 .0019 9.1 2.3:1 3,430 13.1 -- 1.09 ParticleErosion

@ I-19cross section

1):

25 .84 -- 10/03/83 45,000 .0011 9.5 1.9:1 2,780 16.2 -- .65 ParticleErosion

EsperanzaCreek:

26 1.0 2.63 10/03/83 12,700 .0171 8.1 1.5:1 743 17.1 /--

-- 8.64 Translat. Slide&ParticleErosion

SantiumRiver Near

Albany, OR.27

28

1.3 2.66 10/27/82

12/26/80

7,440

61,000

.002

.0030

21.5

28.9

2:1

2:1

2,180

4,190

3.41

14.6

5.20

--

.27

5.41

No Damage

No Damage

Site MeasurementNumber

D50(ft)

SpecificGravity

Gs



(ft3/s)

WaterSurfaceSlope

sw

Depthmax.

d(ftm)

SideSlope

z

AreaA

(ft2)

Velocity Shear(lb/ft2)

PerformanceMean

Va(ft/s)

MaxVm(ft/s)

Hoh River near Forks, WA.:

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Site #1 (old) 2930

1.2 2.69 10/02/8211/04/82

22,0005,060

.00867.0014

19.1014.6

1.2:11.2:1

2,772814

7.946.22/

--9.26

10.31.28

Particle ErosionNo Damage

Site #1 (new) 1.3 2.59 DATA NOT AVAILABLE Particle Erosion

Site #2 3132

1.2 2.48 1/12/7911/03/82

51,6002,140

.00058.006

20.99.4

1.6:11.6:1

4,943608

10.443.52/

--5.57

.76

.35ParticleErosion

No DamageYakima R. @

Cle Elum,WA.

3334

1.5--

2.82--

2/22/8211/05/82

22,2002,660

.0024

.003712.26.5

2:12:1

1,783266

12.4510.0

----

1.831.50

No DamageNo Damage

SacramentoRiver @ E-10near, Chico,

CA.

3536

.54 2.72 1/13/834/14/82

77,00056,000

.000364.00030

28.1023.5

3:13:1

12,6519,610

6.105.83

--7.92

.638.44

No DamageNo Damage

SacramentoRiver @ E-10near Chico,

CA.

373839

.51

.51

.51

2.602.602.60

12/15/8112/23/831/27/83

27,70078,00098,000

.00064

.00081

.00042

20.331.313.0

1.8:11.8:11.8:1

4,32010,70014,600

6.417.36.7

8.54----

.6001.58.341

No DamageParticle ErosionParticle Erosion

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Table 12. Riprap Relationship Calibration DataSite Meas.

No.d50(ft)

SpecificGravity

Slope(ftft.)

BankAngle

K1*/K1(Ss-1)

S/ AverageDepth

(ft)

d50/Davg Per.

Sacramento@Princeton, CA .

1 0.48 2.95 0.00091 37.6 0.4105 0.001136 35.7 0.0134 ND

Sacramento@ Colusa, CA .

2 0.67 2.77 0.00006 27.8 0.7171 0.000047 27.6 0.0243 ND

Truckee River@Reno, NV.

3 2.1 2.65 0.00625 33.5 0.5653 .006700 9.6 0.2188 ND

Truckee River@ Sparks, NV.

5 0.71 2.68 0.0022 29.0 0.6892 0.001899 8.9 0.0798 ND

Pinhole CK. @XS #4

9 2.3 2.8 0.0172 24.5 0.7848 0.012175 5.2 0.4423 ND

Donner Ck. @Truckee, CA.

10 0.68 2.65 0.0062 24.5 0.7848 0.004787 3.4 0.2000 ND

E.F. Carson R. @Markleeville

11 2 2.36 0.01224 33.5 0.5653 0.015919 5.7 0.3509 ND

Walker R.,Coleville, NV. @#2

12 1.4 2.65 0.0181 37.6 0.4105 0.026720 3.7 0.3784 ND

Russian R. NearCloverdale, CA.

14 0.69 2.78 0.00312 24.5 0.7848 0.002233 14.7 0.0469 ND

Cosumnes R. @Dillard Rd.

#1

151617

0.690.780.78

2.782.792.79

0.00180.000730.00076

24.523.523.5

0.78480.80300.8030

0.0012880.0005070.000528

5.819.918.7

0.11900.03920.0417

NDNDND

Rillito Cr. @ CS #1 22 0.84 2.74 0.0162 26.6 0.7431 0.012528 10.1 0.0832 NDSantiam R. NearAlpany, OR.

2728

1.31.3

2.662.66

0.00020.003

26.626.6

0.74310.7431

0.0001620.002431

14.019.5

0.09290.0667

NDND

Hoh R. @ Site #1(old) 30 1.2 2.69 0.0014 39.8 0.2913 0.002843 9.0 0.1333 NDHoh R. @ Site #2(new) 32 1.2 2.48 0.0006 32.0 0.6106 0.000663 7.3 0.1644 NDYakima R. @ CleElum, Wa.

3334

1.51.5

2.822.82

0.00240.0037

26.626.6

0.74310.7431

0.0017740.002735

7.92.4

0.18990.6250

NDND

Sacramento R.@ Peterson B.

35

36

0.54

0.54

2.72

2.72

0.000364

0.0003

18.4

18.4

0.8817

0.8817

0.000240

0.000197

8.9

17.4

0.0607

0.0310

ND

NDSacramento R.@ E-10 37 0.51 2.6 0.00064 29.1 0.6868 0.000582 14.7 0.0347 NDTruckee R.@ Reno, NV 4 2.1 2.65 0.0089 33.5 0.5653 0.009541 11.3 0.1858 PETruckee R.@ Sparks, NV. 6 0.71 2.68 0.00219 29.0 0.6892 0.001891 10.7 0.0664 PE 7 0.71 2.68 0.0055 29.0 0.6892 0.004749 12.2 0.0581 PEPinhole Creek @xs #3

8 0.55 2.85 0.0049 26.6 0.7431 0.003564 5.0 0.1100 PE

Walker R. @ xs #4 13 0.8 2.61 0.01636 33.5 0.5653 0.017974 2.9 0.2759 PERillito Cr. @ CS #3 23 0.51 2.69 0.0038 21.8 0.8318 0.002703 10.4 0.0490 PE

Santa Cruz R. @ CS #3 24 0.65 2.71 0.0019 23.5 0.8030 0.001383 10.5 0.0619P EREsperanza Creek 26 1 2.63 0.0171 33.5 0.5653 0.018556 6.8 0.1471 PE

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Appendix C Chart 2

Chart 1. Riprap Size Relationship

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Appendix C Chart 2

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Chart 1 Appendix C Chart 3

Chart 2. Correction Factor for Riprap Size


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Chart 3. Bank Angle Correction Factor (K1) Nomograph


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Chart 4. Angle of Repose of Riprap on Terms of Mean Size and Shape of Stone


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Chart 5. Conversion from Equivalent D50 in meters to W50 in kg

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Chart 6. Nomograph of Deepwater Significant Wave Height Prediction Curves (modified fromreference 29)

Metricated and English Charts Below:

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Chart 7. Hudson Relationship for Riprap Size Required to Resist Wave Erosion

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Chart 7 Appendix C

Chart 8. Wave Run-up on Smooth, Impermeable Slopes (modified from reference 29)

Chart 7 Appendix C

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Table 9. Correction for Wave Run-UpSlope Surface Characteristics Placement Method Correction factor

Concrete Pavement -- 1.00Concrete Blocks

(voids < 20%)fitted 0.90

Concrete Blocks(20% < Voids > 40%)

fitted 0.70

Concrete Blocks(40% < Voids > 60%)

fitted 0.50

Gobi Blocks fitted 0.85 - 0.90Grass -- 0.85 - 0.90

Rock Riprap (angular) random 0.60Rock Riprap (round) random 0.70

Rock Riprap (hand placed or keyed) keyed 0.80Grouted Rock -- 0.90

Wire enclosed rocks/Gabions -- 0.80

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Appendix C Form 2

Form 1. Riprap Size-Particle Erosion

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Appendix C Form 2

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Form 1 Appendix C Form 3

Form 2. Riprap Size-Wave Erosion

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Form 3. Material Gradation


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Form 4. Roughness Evaluation

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Form 4 Appendix C

Form 5. Filter Design

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Form 4 Appendix C

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List of Charts & Forms for HEC 11-Design of Riprap Revetment (Metric)


Chart 1. Riprap Size Relationship

Chart 2. Correction Factor for Riprap Size

Chart 3. Bank Angle Correction Factor (K1) Nomograph

Chart 4. Angle of Repose of Riprap on Terms of Mean Size and Shape of Stone

Chart 5. Conversion from Equivalent D50 in meters to W50 in kg

Chart 6. Nomograph of Deepwater Significant Wave Height Prediction Curves (modified from reference 29)

Chart 7. Hudson Relationship for Riprap Size Required to Resist Wave Erosion

Chart 8. Wave Run-up on Smooth, Impermeable Slopes (modified from reference 29)

Form 1. Riprap Size-Particle Erosion

Form 2. Riprap Size-Wave Erosion

Form 3. Material Gradation

Form 4. Roughness Evaluation

Form 5. Filter Design


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List of Equations for HEC 11-Design of Riprap Revetment (Metric)


equation 1

equation 2

equation 3

equation 4

equation 5

equation 6

equation 7

equation 8

equation 9

equation 10

equation 11

equation 12

equation 13

equation 14

equation 15

equation 16

equation 17

equation 18

equation 19

equation 20

equation 21

equation 22

equation 23

equation 24


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References

1. Shen, H. W. et al.,"Methods for Assessment of Stream-Related Hazards to Highways and Bridges,"U.S. Department of Transportation, Federal Highway Administration, FHWA/RD-80/160, Washington, D.C., March 1981.

2. Leopold, L.B. et al.,Fluvial Processes in Geomorphology,W. H. Freeman and Company, San Francisco, 1964.

3. Lane, E.W.,"Design of Stable Channels,"Transactions, ASCE, Vol. 12, 1955.

4. Brown, S.A. et al.,"Stream Channel Degradation and Aggradation: Analysis of Impacts to Highway Crossings,"U.S. Department of Transportation, Federal Highway Administration, FHWA/RD-80/159, Washington, D.C., March 1981.

5. Richardson, E.V. et al.,"Highways in the River Environment, Hydraulic and Environmental Design Considerations,"prepared for Federal Highway Administration, National Highway Institute,Office of Research and Development, Office of Engineering, September 1974.

6. Blodgett J.C., and McConaughy, C.E.,"Evaluation of Riprap Design Practices," Volume 2 of "Rock Riprap Design for Protection of Channels Near HighwayStructures,"U.S. Geological Survey, Water-Resources Investigations, Report 86-4128,Prepared in cooperation with the Federal Highway Administration, 1986.

7. Masch, Frank D.,"Hydrology", HEC No. 19,U.S. Department of Transportation, Federal Highway Administration, Washington, D.C., 1984.

8. Corry, M. L., Jones, J.S., and Thompson, P.L.,"Design of Encroachments of Flood Plains Using Risk Analysis", HEC No. 17,U.S. Department of Transportation, Federal Highway Administration, Washington, D.C., 1981.

9. Chow, V.T.,Open-Channel Hydraulics,McGraw-Hill, New York, 1959.

10. Simons, Daryl B., and Senturk, Fuat,Sediment Transport Technology,Water Resources Publications, Fort Collins, Colorado, 1977.

11. U.S. Department of AgricultureSoil Conservation Service - Engineering Division, National Engineering Handbook - Section 5 - Hydraulics,U.S. Department of Commerce National Technical Information Service

12. Richardson, E.V., Simons, D.B. et al.,"Highways in the River Environment, Hydraulic and Environmental Design Considerations,"Prepared for Federal Highway Administration, National Highway Institute,Office of Research and Development, Office of Engineering, September 1974.

13. Jarrett, R.D.,"Hydraulics of High-Gradient Streams,"Journal of the Hydraulics division, ASCE, Vol. 110, No. 11, November 1984.

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14. U.S. Army Corps of Engineers,"Hydraulic Design of Flood Control Channels,"Engineers Manual EM-1110-2-1601.

15. Blodgett, J.C."Hydraulic Characteristics of Natural Open Channels," Volume 1 of "Rock Riprap design for Protection of Stream ChannelsNear Highway Structures,"U.S. Geological Survey, Water-Resources Investigations Report 86-4127,prepared in cooperation with the Federal Highway Administration, 1986.

16. "Methods and Practices of the Geological Survey",U.S. Government Printing Office, Washington, D.C., 1943.

17. Arcement, G. J., and Schneider, V. R.,"Guide for Selecting Manning's Roughness Coefficients for Natural Channels and Flood Plains,"FHWA-TS-84- 204, U.S. Department of Transportation, Federal Highway Administration, Washington, D.C., April 1984.

18. Brown, Scott A."Streambank Stabilization Measures for Highway Engineers,"U.S. Department of Transportation, Federal Highway Administration, FHWA/RD-84/100, July 1985.(Available through National Technical Information Service, Springfield, VA 22161)

19. California Department of Public Works, Division of Highways,"Bank and Shore Protection in California Highway Practice," 1970.

20. U.S. Army Corps of Engineers,"Design of Coastal Revetments, Seawalls, and Bulkheads,"Engineering Manual EM-1110-2-1614, April 1985.

21. Shields, A.,"Anwendung der Aehnlichkeits-Mechanik und der Turbelenzforschung auf die Geschiebebewegung, "Preussiche Versuchsanstalt fur Wasserbau und Schiffbau, Berlin, Germany, 1936.

22. Gessler, J."Beginning and Ceasing of Sediment Motion," in River Mechanics,Hsieh Wen Shen, ed., P.O. Box 606, Fort Collins, Colorado, 1971.

23. Brown, S. A.,"Calibration of a Riprap Design Method,"Summary Report, Sutron Corporation Report No. SCR87-0001,Federal Highway Administration Open File Report, Washington, D.C. 1987.

24. Hudson, R.Y.,"Laboratory Investigations of Rubble-Mound Breakwaters,"Proceedings of the Waterways and Harbors Division, American Society of Civil Engineers, Vol. 85, No. WW3, 1959.

25. U.S. Army Corps of Engineers,"The Streambank Erosion Control Evaluation and Demonstration Act of 1974, Section 32, Public Law 93-251: Final Report toCongress,"Main report and Appendices A through H, December 1981.

26. Christopher, Barry R., and Holtz, Robert D.,"Geotextile Engineering Manual,"Prepared for the Federal Highway Administration, National Highway Institute, Washington, D.C., March 1985.

27. Galloway, B.M.,"Pavement and Geometric Design Criteria for Minimizing Hydroplaning,"Texas Transportation Institute, Texas A&M University,Prepared for the Federal Highway Administration, Report No. FHWA-RD-30, December 1979.

28. Chen, Y.H., and Cotton, G.K.,

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"Design of roadside Channels with Flexible Linings,"Hydraulic Engineering Circular No. 15,Prepared for the Federal Highway Administration, Washington, D.C., 1987.

29. Department of the Army,"Shore Protection Manual",Coastal Engineering Research Center, Waterways Experiment Station, Vicksburg, Mississippi, Fourth Edition, 1984.(Available from the Superintendent of Documents, U.S, Printing Office, Washington, D.C.)

30. Standard Specifications for Highway Bridges,American Association of State Highway and Transportation Officials, 13th edition, Washington, D.C., 1983.

31. Land slides: Analysis and Control Special Report 176 (1978)Transportation Research Board National Academy of Sciences.

32. Department of the Army, Corps of Engineers,Investigation of Filter Requirements for Underdrains, Waterways Experiment Station, Tech. Memo No. 183-1, Vicksburg,Miss., December 1941.

33. Anderson, A.G., Paintal, A.S., Davenport, J.T.,"Tentative Design Procedure for Riprap Lined Channels,"Highway Research Board, NCHRP Report Number 108, 1970.

34. Barnes, Harry H.,Jr.,"Roughness Characteristics of Natural Channels",Geological Survey Water-Supply Paper, U.S. Department of the Interior, 1849.

35. Maynord, Stephen T.,"Stable Riprap Size for Open Channel Flows,"Dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy, Colorado StateUniversity, Fort Collins, Colorado, Summer 1987.

36. Wang, S.Y., Shen, H.W.,"Incipient Sediment Motion and Riprap Design,"Journal of the Hydraulics Division, ASCE, Vol. 111, No. 3, March 1985.

37. U.S. Department of Transportation,"Design Charts for Open-Channel Flow," Hydraulic Design Series No. 3,Federal Highway Administration, August 1961, reprinted November 1977.

38. FHWA/USGS Bridge Waterways Analysis Model: Research Report No. FHWA-RD-86- 108,Washington D.C.,1986. Unpublished draft users manual for WSPRO.

39. Hydrologic Engineering Center,HEC-2, Water Surface Profiles,November 1976, Davis, CA

40. Bradley, Joseph N.,"Hydraulics of Bridge Waterways,"Hydraulic Design Series No.1, Federal Highway Administration, Second Edition, March 1978.

Appendix D References : Hec-11

1. Chow, V.T.,Open-channel hydraulics,McGraw-Hill, New York, 1959.

2. Shields, A.,"Anwendung der Aehnlichkeits-Mechanik und der Turbelenzforschung auf die Geschiebebewegung,"Preussiche Versuchsanstalt fur Wasserbau und Schiffbau, Berlin, Germany, 1936.

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3. Blodgett, J.C.,"Hydraulic Characteristics of Natural Open Channels," Volume 1 of "Rock Riprap Design for Protection of Stream ChannelsNear Highway Structures,"U.S. Geological Survey Water-Resources Investigation Report 86-4127,Prepared in cooperation with the Federal Highway Administration, 1986.

4. Anderson, A.G., Paintal, A.S., and Davenport, J.T.,"Tentative Design Procedure for Riprap-lined Channels"National Cooperative Highway Research Program Report 108, Highway Research Board, 1970.

5. Strickler, Alfred,"Some Contributions to the Problem of the Velocity Formula and Roughness Factors for Rivers, Canals, and Closed Conduits,"Bern, Switzerland, Mitt. Eidgeno Assischen Amtes Wasserwirtschaft, 1923.

6. Norman, J.M.,"Design of Stable Channels with Flexible Linings,"U.S. Department of Transportation, Federal Highway Administration, Hydraulic Engineering Circular No. 15, 1975.

7. Maynord, S.T.,"Practical Riprap Design,"Miscellaneous Paper H-78-7, Hydraulics Laboratory,U.S. Army Engineer Waterways Experiment Station, Vicksburg, Miss., 1978.

8. Blodgett, J.C., and McConaughy, C.E.,"Evaluation of Riprap Design Procedures," Volume 2 of "Rock Riprap Design for Protection of Stream Channels Near HighwayStructures,"U.S. Geological Survey Water-Resources Investigation Report 86-4128Prepared in cooperation with the Federal Highway Administration, 1986.

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Symbols

A, C, D, G, H, K, N, P, Q, R, S, T, V, W, Z, MISC.

To jump to a specific part of the alphabet, click on the above HotLinks!Click the Back button to return to the top of this page.(If the letter you are looking for does not appear in the HotLink list below, then there are no glossary entries for that letter!)

AA = Flow area m2

CC = Coefficient that relates free vortex motion to velocity streamlines for unequal radius of curvature.

Dda = The average channel flow depth (m).

D50 = The median bed material size (m).

D15 = The fifteen (15) percent finer particle size (m).

D85 = the 85 percent finer particle size (m).

Gg = Gravitational acceleration (m/s2).

HH = The wave height (m).

KK1 = A correction term reflecting bank angle.

Nn = Manning's roughness coefficient.

nc = Composite roughness.

n1 = The roughness of the smoother lining in composite roughness evaluation.

n2 = Roughness of rougher lining in composite roughness evaluation.

PP = Total wetted perimeter of channel section.

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Pmc = Wetted perimeter of channel bottom in the zone of main channel flow.

QQmc = Discharge in the zone of main channel flow (m3/s).

Qs = The sediment discharge.

RR = The hydraulic radius (m).

Ro = The mean radius of the channel centerline at the bend (m).

SSf,S = Friction slope or energy grade line slope.

SF = The stability factor.

SP = The Shield's parameter.

Ss = The specific gravity of the riprap (solid) material

TT = The topwidth of the channel between its banks (m).

VVa = Mean channel velocity (m/s).

WW50 = The weight of the median particle (lb N)).

ZZ = Superelevation of the water surface (m).

MISC.γ = The unit weight of water (9807 N/m3).

γs = The unit weight of the riprap (solid) material (N/m3).

θ = The bank angle with the horizontal.

τd = The driving shear stress (N/m2).

τr= The resisting shear stress (N/m2).

φ= The riprap materials angle of repose.

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